You can have a spray tan before going on holiday but please bear the following in mind:
A spray tan offers no protection from the sun - you will still burn/tan etc. If you want to prevent sun-damage then you will still need to apply protection. Some lotions/oils/creams can accelerate the tan coming off, especially if they contain mineral oils.
The more you're in the water, the quicker your tan will come off - when you come out of the water, pat your skin dry, or dry off naturally if you can bear it. Do not rub your skin as exfoliation of any sort will seriously shorten its life.
Make sure your skin is moisturised to the max the week before going for your tan as that will help to to last longer. Don't apply moisturiser or shave 24 hours before your tan.
Keep your skin moisturised after your tan - it helps to prevent the natural shedding of skin cells. If possible, avoid moisturisers with mineral oils as this will strip the tan faster than you can say tango
You can buy a Nivea mineral free moisturiser in any supermarket for a very reasonable price.
Some fake spray tans last longer than others - I use two that last at least 6 days.
littlemissnormal "^ haha yep re the white under bum bits! The lady who sprays me gets me to bend forward to prevent this and also makes sure she gets the bits under my boobs!"
I always get my clients to lift their legs slightly when doing their "smile line" under the bottom - it's less embarrassing for them than bending over and shoving their bottom in your face 