Listen for sounds before the oil pressure gague indicator rises. If it is a problem with pressure not building quickly enough, it might accelerate wear on the timing chain and valve lash adjusters. Enough folks have said the lag is normal but just be aware of noises you haven't heard before.

FWIW, I miss my 78 450SEL which would regiter oil pressure while cranking.

Sixto
91 300SE
87 300SDL
81 300SD (on ebay)