I've bought premium before just to be clear. I was about to purchase premium again and it says 50 credits offered? Does this still apply to me even though I have subscribed to become premium before?

NO,
the 50 credits is for 1st Time Premium subscribers only.
One 50 credits offer per Member.
If you had premium in the Past, and received the 50 credits before, this offer does not apply.

Okay cool, thanks for letting me know. I've done the HentaiHeroes thing for 25 credits. I registered using the same email and have subscribed. Do you know how long it takes for the credits to come through?

@Dabber123

I think you Misunderstood

You asked does this Apply to you?
I answered: NO
I answered: the 50 credits is for 1st Time Premium subscribers only.

since you Previously had Premium,
the Offer would not Automatically be Applied.

the 50 credits is for 1st Time Premium subscribers only.
One 50 credits offer per Member.

It's ok.
But it also should be explicitely and clearly stated on the offers' page (and it is not, at the moment).