Windows XP slow to boot 1st thing in morning

Windows XP pro is very slow on 1st boot up in morning. (20 minutes) PC is then very slow.
On restart PC boots normal (90 seconds) and PC speed is normal.
I’ve run hardware diag. and all is good. (run diag. several times now) I’ve checked for malware – none. PC is very clean.
Any ideas before I do a clean reinstall?