If SPX is going down there is a good chance that VIX is going to print a big rally in the following 2-3 days.
It's never a good idea to sit in TVIX and wait for a bounce.
You need to time almost perfectly when it is starting to run. VIX can easily print x2, x3 prices.
I suggest an entry here at the inverted hammer. Stop can go below today's low...