IDK for sure, but the "deeper" parts of silicone can be still not cured all the way so I'm gonna give it like 3 days or so ...
and no it's not that hard ... it's not quantum physics =) just like someone mentioned have the glass nicely cut, make sure that the sides are a BIT smaller than the exact space bwt the glass cuz I guess u wanna put like ... 1/16 of silicone btw the side and front/back wall ... I'm not a glacier nor a aquarium builder yet I made this and I'm very confident that it will hold water well ... ( the ge silicone is SO strong ... )