When is it safe to be around the fumes from a newly varnished floor?

Q: When is it safe to be around the fumes from hardwood floor refinishing / varnish? 

A: A chemist tells me that generally for both solvent

and water borne finishes, the solvents used are dissipated in 24 hours. Solvent based coatings can be dry enough to walk on in 8-10 hours and water borne in 1-2. Drying and hardness curing are not the same thing however. Both coatings will continue to get harder or cure, and depending which finish is used can take from 24 hours to 4 weeks.