Lawn re-dressing after Spring scarifying & reseeding

Done the Spring scarifying, reseeding and dressing with sand, topsoil & loam etc.
How soon could I spread another dressing of sand, topsoil & loam etc as above without scarifying and reseeding to help the lawn in summer months.

 

I would wait at least until the seed has germinated and grown enough so that it is firmly anchored by its roots so that won't be disturbed by spreading more soil etc, and the new grass has long enough leaves that they will still have a decent amount showing above the dressing.