Let me ask: If they are going to explode,
>how long after they are capped do
>they start to blow?
It depends on a lot of factors, so it's impossible to predict when bottles might explode, if they're going to. Temperature and wild yeast/bacterial infections can play a part.
It's a far better policy to prevent bottle bombs in the first place. Make sure your processes are clean (sanitize, sanitize, sanitize) and be certain fermentation is complete before bottling (get a hydrometer and use it).
Happy brewing, Brina