I have a tiny, 3mm, black spot on the top of my wrist w/ a little gray in it. since it's so small do i have to have it checked or can it wait?

Depends: If its a new spot or an old spot which is changing colour, change in sensation or change in size or you are concerned then you should see doctor and get dermoscopy.

Get it checked out: Even though the spot seems small, it's always best to have it looked at, especially if it's new or changing in any way. Spots that are darker in pigment, have irregular borders or asymmetry are also more concerning. Most physicians would recommend a full skin exam every 1-2 years to screen for skin cancer but don't wait until your next visit if this spot is new.