How much time are we talking about? Some passengers appear to spend ages in the loo while others are in and out in seconds. Your "time frame" will also be based on your history. The only time this really will be an issue is whe there is only one loo or the cabin crew wish to secure the cabin for landing.
With regard to the selt belt sign I totally disagree with SoS. Insurance is not and never ever will be an issue. All passengers are insured at all times. The problem is that the seat belt sign is a lawful command issued to ensure the safety of passengers. When on all passengers should remain seated (?) with their seat belts on. It is unlikely to be an issue unless you have chosen the wrong day to go flying.