Depends on lots of things, mostly the tenderness of the weeds and the rate you used. Soft fast growing stuff may be fine. I think two weeks is recommended before disking, not sure about mowing. I would wait at least 5-7 days if I had ideal conditions(good soil moisture and reasonably warm).
Why would mow something you have sprayed with roundup?
Seed will probably come up better with the weeds standing, better soil contact, and it will have some mulch in a couple weeks.