The active ingredient in tan accelerators is Tyrosine, or Psoralen (extracted from citrus oil) along with vitamin E and copper, these ingredients kick start the melanocytes, which are situated in the basal layer of the skin, to produce melanin in a process called melanogenesis, which makes them come to the surface.

Under normal circumstances, the process of melanin production takes quite a long time and UV light naturally kick starts the natural chemical process.
We use tan accelerators to speed up this process by tricking the melanocytes into action by the use of Tryrosine or Psoralen.....it's a complicated subject to explain,....however, very briefly, we all have about the same amount of melanocytes in our bodies, but the pigment they contain differs, one is a brown pigment and the other is a yellow/red pigment.

This explains why pale redheads never or hardly tan and people having the brown pigment do, it doesn't matter how much melanin you produce, if your DNA make-up doesn't contain the brown pigment, you won't go the same colour as the people who do have the brown pigment, and all you will be doing is bringing to the surface the type of melanocytes that you possess in your genetic make-up.
In some races the melanocytes are active all the time, with or without sunshine, hence brown and black people.

So, it doesn't matter when you apply the tan accelerator, but it would be a complete waste of money and time, if you were not planning on getting some sun exposure after its application at some point"¦.Elemis say to use daily, for 2 weeks before your holiday, so during this period, this would bring the melanocytes to the surface in preparation for the sun exposure that you expect to get during your holiday.

If your experiencing grittiness, then that indicates to me, that the two products being used, are not mixing very well, it may be something in either product that is causing the grittiness or you haven't given enough time for the accelerator to be fully absorbed, I always used my accelerator in the evenings after a shower, then I would wait before applying a moisturiser, but most tan accelerators incorporate a moisturising ingredient into the concoction these days.

Here's a thought for you"¦.melanin production is stimulated by the amount of light the optic nerve is exposed to, and the optic nerve is "tied" to the pituitary gland, which is also involved in the production of melanin, so apparently people who wear sunglasses don't tan as good as those who don't....I haven't tested it myself and don't plan on doing so either, the skin around the eyes is paper thin and needs protection.

Sanji