If I apply drylock to block wall will it crumble in years to come?

You have to prep properly. There is an etch that has to be done for Drylock to stick. Without the etch,

If you don't have the time to do it right, when will you have the time to do it over?.

It's a LOT more work to do it over. Trust me.

The etching is the nasty part of the job. Drylock's version is a powder that you mix with water. It's very acidic and generates nasty vapors in an unventilated space and will ruin your clothes. Safety glasses, gloves and adequate ventilation are necessary.

The other stuff to use is muratic acid which ia a dilute hydrochloric acid.

Rinse well.

If you have to patch anything, Rockite works.