Weir and silicone ??s

I am going to be adding an internal coast to coast in my DT. my plan is to drop the water level, use heaters and powerheads to move water around until silicone is cured. Question is, how long is that? is there a brand that cures quicker than others? thanks.

 

Is it already drilled?
I think most silicone takes 24 hours to cure. A lot of people I see use ge silicone 1. I read a tube and nowhere did I see aquarium safe. I did see where it said not for aquarium use.. Maybe that's there for liability? I used loctite silicone for my sump. It said aquarium safe and found it in the epoxy area at lowes. Took 24 hours to dry.