I'm currently using retin-a topical gel 0.25% can I also use a tanning bed while using the cream? Or how soon can I?

Any benefit you are getting from your Retin-A will be decimated by your tanning bed use.  Tanning bed users look older earlier and get many more skin cancers.  Furthermore, Retin-A's effect will remove parts of your dead layer of skin which will make your skin more sensitive to ultraviolet damage.  If you are looking to improve your looks, quitting the tanning bed is the only option.

You don't want to be in the sun - and especially not tanning beds - if you are using Retin A. Plus, I'm not even sure why you want to use a tanning bed anyway - you are defeating the results of using Retin-A and making yourself more susceptible to aging skin and skin cancer. "This answer has been solicited without seeing this patient and cannot be held as true medical advice, but only opinion. Seek in-person treatment with a trained medical professional for appropriate care."