I hit my head and have a small bump i am a little dizzy how long should i wait before going to sleep?

You describe an area of superficial bruising, and a vague comment of "little dizzy". Not feasible to objectify this, but if you do not have an increasing headache, nausea, vomiting, loss of balance, loss or doubling of vision, progressive numbness or weakness, confusion; appears to be no reason you should avoid sleep. If you feel unwell, a visit to urgent care might be reassuring.