Oops. That's got to suck.
Silicone skins over in about ten or twenty minutes, depending on the relative humidity and the temperature you're working in. But it won't stop off gassing until it's cured, which is again somewhat dependent on relative humidity, but more so on temperature.
If you're in a hurry to cure silicone and it's possible to apply heat, it will speed up the cure quite a bit. A heat gun or even hair dryer on high will assist in faster cure times. Use some care, heat gradually, to avoid overheating the glass too quickly, which could cause shock breakage. And obviously you must take care to allow glass that's been heated to cool completely before you add water, that same temperature shock will break glass just as badly as a poorly swung wrench will
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Incidentally, you can use crazy glue to glue some decor, such as rocks, together and it cures in almost no time. Once dry, perfectly tank safe. Some use it to glue coral frags, some use it to glue moss or plants to rocks or wood too.
There are also two part epoxy putties that are entirely safe. Some are made for aquaria, mainly aimed at salt water tanks but safe for FW too. Usually come in a reddish and a slate blue colour, to match live rocks or coral. Slow cure, about twenty minutes of working time before it begins to harden. This will cure even under water, which is pretty cool, though I found it was a bit of a hassle to get it to stick reliably to wet rocks. It would appear to be stuck and then the pieces would come apart weeks or sometimes just days later. So I prefer to use it dry.
But there's a type made for plumbers too, that's tank safe. It's 100% safe for potable water systems, and safe for fish and other aquatic inhabitants, though this is known because folks have tried it, not because it says so on the label. I've used it with fish, shrimp and snails, and had no problems. I'll have to go find the brand name I personally know is safe.
Its main disadvantage is a fast cure time, only two or three minutes before it hardens, so you must have all your pieces arranged and ready to assemble fast, and its tan colour won't match a lot of things, so depending how you use it, it may show up more than you'd like it to. But it's very cheap compared to the aquarium specific type of epoxy putty.
Edit. the brand I'm familiar with is called Oatey's. Home Depot has it here, it's made in the USA.