Thanks very much for your reply. This has solved the delay following log in.
However, I had an awful time restarting after running first aid - my mac would not accept my correct password. After an hour of stress thinking that i had somehow been locked out, i discovered that when booting up High Sierra now wants your iCloud password first (without prompting that this is what is required), then takes you to a second login screen where it needs your apple id password. Why does this happen? Can I stop it from happening? It seems like iCloud is a nuisance, but I'd like to use find my mac. is there any way of using find my mac without iCloud?
Thanks