If it is a song, and it is delayed for 0.5 or 1 second, it really does not matter. What I am trying to find out is for games and videos. If there is a 0.5 second audio delay, for videos (movies or youtube if video/audio is unsync’ed) or for games, then it could be a bigger problem.
There is zero concern for music and videos since the system compensates for audio delay. Same for many games since as long as the visual and audio tracks start at the same time (buffering enough content for each to start and then hoping the new content delivery / creation can keep the buffer from emptying).
Now, technically speaking, the laws of physics and the limited processing power of the CPU/chips that encode/decode the audio ensures there is a delay - but it's not on the order of a second. Subjectively, this isn’t a problem for me until I use airplay / WiFi and even then it’s nit horrible but the lag is noticeable. But I also can’t argue if someone else has a subjectively different experience and the lag isn’t acceptable to them.
The codec and stream of the bluetooth chips means that the sound needs to be buffered, encoded, transmitted, decoded and then sent through the amplifier.
There have been some nice attempts to scientifically measure this - http://stephencoyle.net/airpods/
The raw data says the measured latency of wired headphones is around 85 ms and AirPods are around 256 ms. My personal impression is the AirPods are more in the range of 120 ms delay and almost equivalent to wired earphones. Also, I'm fairly certain that Apple corrects for video playback if you use the API since I've never ever gotten the feeling that videos lag when switching from AirPods to EarPods and back on Apple devices and Apple audio devices.
Same sort of synchronization is being done for the HomePod setup where millisecond sync and offset is going to be used to synchronize and phase the sounds for multiple bluetooth playback speakers spread around a room, but that's a far easier task where you can buffer all the sounds and then play a delayed and perfectly synchronous to the phase of the sound waves - as opposed to having a low latency audio interface.
You'll want custom hardware for that like the Universal Audio Arrow line of monitor hardware if you are performing live or making millisecond measurements.
The only case where I've seen lag as a legitimate problem is musicians with split second timing needs or scientific measurement apps. I've also heard of AirPods and iPhones needing a restore if they get stuck or some process is running amok and otherwise slowing down the processing of audio.
Yes they have a delay, just as traditional headphones have a delay (albeit practically imperceptible). It's caused by both the digital to analogue conversion, as well as the variable amount of time it takes the signal to be transmitted and any interference present.
If you're using bluetooth headphones (airpods or otherwise) while playing video, Apple and most manufacturers adjust the audio based on the latency so they remained synced. They also buffer all audio ahead a certain amount (when possible) to deal with small inconsistencies in the connection.
Assuming the application is using Apple's native support for this, the latency correction is built in. Any time you see the iOS or macOS styled video player you don't have to worry. Applications with their own custom players will have to deal with this more manually, and so support is not guaranteed. (e.g. Youtube on Chrome in macOS has a barely-noticable audio lag).
Unfortunately with games there isn't really anything they can do to make it better synced. Though since you probably have the device directly in front of you, you're in a pretty ideal position to limit any lag. At that point the amount of lag depends on the devices and distance/interference (which according to @bmike's answer, is pretty low for AirPods).
Noticeable Delay When Using For Phone Calls.
Watching YouTube videos and what not are okay, sometimes with a slight delay in movement of the lips with the audio you hear. That's annoying but less critical than the following.
When making phone calls with the Airpods on an iPhone (in my case the Xs), there is a noticeable delay between what you say and when the receiver hears it. More than what you're typically used to with other headphones or through the built-in earpiece.
Others might not notice it but it's very obvious to me. That gap of silence between what you say and when they hear it is the cause of many awkward conversations where it feels like you're constantly cutting the other person off. You start talking but they hear silence for a fraction of a second, enough for them to continue on with their sentence. Then your voice comes in and they stop. And on and on it goes.
I used to use my B&O headphones with the 3.5 mm jack in my old iPhone 6, but since "upgrading" to the iPhone Xs that doesn't have the 3.5 mm jack, I'm "forced" to use my Airpods over Bluetooth (unless I buy the Lightning to 3.5 mm adapter).
It's a big step backwards in quality for me. Not sure if other Bluetooth headphones handle this better but if Apple's own Airpods can't do it without a noticeable lag, I doubt others will be better.
Curious to see if others have experienced the same thing and if it's perceptible to them as well.