That's a big beer!
Hopefully the starter was nice and active before you threw it in, and hopefully you aerated the wort very well (pure O2 would be best for that OG).
I also hope and assume you didn't pitch the yeast at a high temperature.
If you did all that, you should have activity within 24 hours.
Otherwise, I still wouldn't get too worried until 72 hours have passed with no activity.
If that's the case, I'd then make a new starter with your additional vial of yeast, and re-aerate the wort well. Pitch and re-commence trying to be patient.