How long, how often, and how soon REMs occur in any particular sleep depends on the sleep circadian rhythm which is governed by your hypothalamus as well as other factors from diet to work to stress to life style and environment.

You can "tweak" it around using various methods including taking supplements but you risk upsetting your body's natural clock , which can result in real physical illnesses.

Whatever you decide to do, you should really study into it, know how it works, why it works and the associated risks vs benefits. Dont follow any advice nilly willy without checking it out properly first.