Primer - wait to block?

Depends on the final result your looking for..... When you spray primer the solvents don't fully evaporate in two hours.... Most of it does & you can get adequate results but the truth is the longer you wait the more solvents will evaporate.... While the primer isn't fully cured it will move... If you've seen sand scratch swelling your seeing the effects of solvent trapped while the sanding was done & when released it causes the primer to swell along the scratch lines...

In a production shop they push the work through... Most customers either won' notice sand scratches when they appear a month later or simply won't want to deal with the matter....

If you have time letting the primer fully cure offers a better long term result...