You should leave bleach in your shower for no longer than 10 to 15 minutes. The use of bleach causes numerous hazards. Sure, it is an excellent germ killer and can be used to great effect in cleaning your home. However, it can also cause damage to any surface it touches, it can cause skin irritation, it can irritate your lungs, and the fumes can give off headaches. You can also get a very nasty chemical burn if the bleach comes into contact with your bare skin.
When used on your shower base, and even hardy porcelain surfaces, it can strip away layers and leave discoloration marks. For this reason, you should never leave bleach, especially neat bleach (neat bleach is a bleach that has not been diluted with water but instead poured straight out from the bottle) on a surface overnight, or even more than 15 minutes.
When you are using bleach you should always follow the exact instructions given on your bottle. If it states that you need to dilute it, then do this using the exact amount they say. You should wear gloves and protect any visible skin. You should also take care not to get it on your clothes as it can ruin the material by dyeing it.
Always keep your bathroom window wide open to let in fresh air if you have put bleach in your shower. Leave the room whilst it is down, and always clean it up well, rinsing it with water after the 10 to 15 minutes is up.