Meta is telling developers that the ideal VR session length with today's hardware is 20-40 minutes, and has explained its reasoning.In a blog post for developers, the company explains that sessions must be "long enough to deliver on a satisfying amount of progress", but not so long as to run into "current form factor limitations on how long people can continuously stay in their headsets"."In general, we recommend building VR games that are optimized for the 20-40 minute “Goldilocks” zone so users don’t need to choose between “quitting in the middle of something” or pushing themselves past their comfort levels."Sessions shorter than 20 minutes, Meta explains, don't justify the friction of putting on a headset. Specifically, they don't deliver enough "progress, engagement or entertainment to validate the decision to engage with VR", including clearing physical space and donning the headset and controllers.Sessions that drag on for more than 40 minutes, on the other hand, force users to “choose between quitting in the middle of something or pushing themselves past their comfort levels”.Most Quest sessions are shorter than 40 minutes, Meta says, with longer sessions being "special occasions".This is primarily due to the form factor limitations of current hardware, Meta explains. Given the roughly half-kilogram weight of today's Quest headsets, longer sessions can be physically uncomfortable. And current optics (especially the fresnel lenses of the cheaper Quest 3S, we should note) can cause eye strain over longer sessions.Couple this with motion sickness in titles which use artificial locomotion, and "a majority" of users either can't or don't want to stay in the headset for longer than 40 minutes, the company claims.However, this doesn't mean that gameplay loops should be 20-40 minutes, Meta stresses.The company recommends a gameplay loop between 10 and 20 minutes, such that users can complete the loop at least once, getting a sense of satisfaction, and then choose to run through it again.Here are Meta's seven recommendations to developers of how to build for the 20-40 minutes "goldilocks zone":1. Deliver on core expectations of the game within the first 20 minutes of the experience: • Avoid long tutorials or text that may get in the way of delivering this promise in time. Utilize reactive or “Just in Time” tutorials that appear only when you need to teach players necessary skills. • Incorporate as much “teaching” into the actual experience as possible and build early objectives or levels around the mechanics you want to teach early. • Start users off with a few short objectives (e.g., 5-10 minutes) to provide quick wins while they learn. Foreshadow longer term objectives to give players a reason to return. • Progressively teach users controls and gameplay mechanics as part of the initial objective or loop.2. Focus on shorter loops & objectives (10-20 minutes) that chain together into 20+ minute sessions: • Chain shorter progression loops together to create full sessions that allow users to play as long (or as short) as they want. This looks different across game genres: • Round-based multiplayer games: Matches (composed of multiple rounds) should be playable in under 20 minutes. Players can then choose to queue up for another match, or take a break. • Single player games: Ensure levels or objectives can be completed in under 20 minutes with a sense of accomplishment and clear next steps.3. Build in regular breaks every 10-15 minutes: • Allows players to complete non-headset related tasks (e.g. bathroom breaks, getting a drink, talking to someone in their house) without ending their session. • Breaks have been shown to improve session satisfaction if they are non-disruptive to engagement (e.g. they can pause content, sit out a round and jump back in, break between loops, etc.). • Breaks do not reset comfort and should not be used as a stand-in for a satisfying end to a session.4. Build features that make it easy to leave and return later: • Regular autosave so players are confident they can pick up where they left off. • Let players see how long since last save/autosave so they know how much progress they will lose if they leave. • Provide information on progress toward an objective or the next checkpoint so players can decide whether to keep going to take a break. • Clearly remind players of their next checkpoint or objective so it’s easy to pick up where they left off.5. Tailor recurring quest/reward systems to appropriate timelines: • Daily quests should be fully-completable within 20 minutes. Additional quests should provide more time for players to earn them (e.g., providing users a week to complete multiple quests). • Weekly quests should incorporate checkpoints or multiple smaller quests to allow users to make progress over multiple sessions. • Avoid very short mobile-style quests that encourage brief check-ins: VR sessions require a higher payoff per session. Check-ins (e.g. a login reward) should be paired with longer engagement (e.g. a login reward as part of a longer Weekly Quest list).6. If building for Worlds, consider Horizon mobile app cross-screen compatibility: • Balance the need for shorter time frames (5-8 minutes) on mobile devices with the desire for more immersive experiences on other platforms. • Consider quests or tasks that are better reserved for VR or mobile, and build loops that allow people to switch between as necessary.7. In entertainment, ensure there are easy continue or drop in options for users to pick up where they left off. • Save current state so a user can easily resume. • Ensure persistence between sessions. • Encourage users to resume partially-viewed content upon launching the app. • Include easy pause, rewind and reset functions in case the user is interrupted.At the end of the post, Meta notes that ideal session lengths may expand in both directions in the future "as form factors shift and change". The friction needed to don headsets will drop, and the comfort of headsets will increase. But for now, developers will want to build for the hardware as it exists today, optimizing for the very real friction and comfort constraints.