We want to make sure we understand the description of the issue. There are two types of delays you could be reporting here:
A delay between the source and the speakers: In this case all 3 speakers would play in sync with each other, but take several seconds to start or stop relative to the commands in the Bose app or the Bluetooth device playing the music. This type of delay is normal as grouped playback takes significantly more bandwidth and buffering to run correctly
A delay between the speakers: This would involve two or more of the speakers playing out of sync with each other. As long as you are using the "Play everywhere" button in the system tray of the SoundTouch app, all speakers should be able to play music in time with one another. If this is your issue, please let us know so we can assist you in correcting it.
Here are some steps to try in order to resolve this:
Reset all the Bose products involved by unplugging power for 30 seconds
Perform a similar reset to your home router.
If your home uses any additional Wi-Fi hardware (extenders, repeaters, powerline adapters etc.) try elminating or disabling them temporarily and test out the group-playback feature with all devices connected to the main Wi-Fi router.
If any of your speakers are connected by Ethernet, similarly make sure that they connect directly to the router with no hubs, switches, or other hardware in-line between them.
Please try out the resets and let us know if any of the equipment mentioned in #'s 3&4 is part of your setup. Thank you.