What time does the svs event start?

Each Clash event starts at reset, this is at 00:00 on the game clock. You can see the game clock by going to the settings menu. (Tap the three dots at the top of the expanded main menu on the right).

SvS starts at reset on day 6 (Saturday for most people) when the event is active. You will have to compare the game clock with your own time to see how many hours ahead or behind this you are.