Had a cortisone injection yesterday for a shoulder impingment yesterday. Forgot to ask Doc how long to leave it before I lift....or Roll for that matter (bjj as apposes to refer) 
Where was the injection specifically? In the tendon? Or in the joint? What specifically was the doctor trying to resolve? Rotator cuff tendon inflammation? Biceps tendon? Bursa?
Timelines will vary based on where the injection was given and into what structure. Some parts I tell people to give it 48-72 hours or even a week before progressing with any exercise, just to allow the injection to do it's work.
If it is an area where I think it is okay to begin activity soon, I normally tell people VERY LIGHT exercise is okay and nothing plyometric in nature. The injection can dehydrate tissue and leave them more susceptible to tearing if too heavy/explosive of activity is started too soon. I personally would error on the side of caution and not roll for a bit. If you are insistent on staying active, you could perform basic ROM activities or slow, independent (without a partner) technique based bjj drills that are low impact and not explosive movements safely for a bit. Or if in significant uncertainty, call up the doc and ask him for his recommendation.
Shoulder impingement so shot was in joint. I've got MRI Monday so will know full extent after that. I was lifting pretty heavy (for me) and rolling / sparring hard most days up to the day of the cortisone.
Rotator cuff he thinks but waiting on MRI