How long it needs to cure, depends on how thick the bead is. Doesn't hurt to let it go an extra day or two. That silicone should be fine; I have used it. Usually, I will get the house brand from Home Hardware or Rona. Both say aquarium safe on the tube. I used to always buy the Matercraft from CTC which also said "ideal for aquariums" on the tube, but I think they no longer have it.
Join a fish club. Don't have one in your area? Start one.