Can you tell me when I should remove my veil, and also when my mother should take her hat off?
Most brides take off their veils for the reception, but it's not necessary so basically, it's completely up to you. Most veils are secured in the hair with a comb, so are fairly easy to remove. Speak to your hairdresser and make sure you know how to remove the veil without disturbing your hairstyle.
Even at relatively informal weddings, it is usual for the mothers of the bride and groom to wear hats. Ladies in general (not just at weddings), are not supposed to remove their hats during a seated meal at a formal event. Guests will usually take their cue in this respect from the behaviour of the mothers.
The best time for mothers to remove their hats is after the meal when there is usually a short break which enables the ladies to freshen up before the evening reception. This would probably be the best time to remove your veil too as you probably won't have much time before the meal.