My baby is due for 18 months vaccine due to covid neither doc's are open nor it's safe to take him out so for how long it can be extended??

Doctors are readily available specially for vaccination they are taking precautions because vaccination are necessary for babies. Give baby bath after coming back from hospital. Cover his/her face by cotton dupatta. You can delay for 15 days

It can be postponed but few hospitals are opened for the vaccination, so call the Paediatrician and check.