That leak will spread, basically what's happening is the glass panes are being pulled apart over time, under pressure. The silicone finally gave out at that tiny spot and will spread over time as the rest of the silicone is now under extra stress. There is no way you can reseal the silicone using silicone, since it doesn't stick to itself. It only sticks to glass and even if you patched up the entire area with silicone, the only area that will stick is the outer patch on glass, That's assuming you got it squeaky clean, AND scraped off all the silicone. Plus you'd have to wait a few days for the silicone to cure before filling it up again. The center of your patch will really be 2 layers of silicone, not connected. As for how long it takes for the leak to spread? I couldn't say, could be months. You can put a bucket at the corner to capture the leak, indefinitely. you can calculate the leak rate by how long it takes a drop to come out, put a big enough bucket, then go on vacation. Personally I have had 2 tanks leak. The first I patched with another piece of glass and silicone, and filled it up a day later, only to have the silicone give out a month later. The second tank, I didn't bother trying to fix it, I simply replaced it. Took me 2 weeks to get a replacement tank, and the flow at the leak was constant and didn't appear to be getting worst.