Blizzard has primed players in advance that the next Overwatch PTR session which will be coming “very soon”.
The planned November Symmetra changes won’t be included in this update in case you were wondering. Instead, the PTR will be live longer than usual as Blizzard want to “push more significant hero changes”. These changes will be iterated on during this PTR session because they want to “see whats fun and working” before making changes.
There’s no exact date for the PTR going live but “very soon” is about as good as it gets with Blizzard. You can always go and enjoy that great Sombra ARG until it does go live.