How long after initially being concussed should i wait to sleep?

It's ok to go to sleep about 3 hours after a head injury, but we would want, as a precaution, to have someone awaken you every few hours or at least observe you throughout the night.

This short answer from Cleveland clinic website should satisfy you: https://health.clevelandclinic.org/is-it-safe-to-sleep-after-a-concussion/

If you suffered a true cerebral concussion, it is considered a true ACUTE brain injury, and typically it involves loss of consciousness, amnesia, or both. Assuming additional brain injury has not occurred, there is absolutely no reason why you need to avoid sleep. This is an outmoded and disproven concept. But if you are worried, and have symptoms, a visit to an urgent care center might help.