Well, I can’t help as I can’t compare the actual time of loading with the previous ones.
I’ve reinstalled Windows 8.1 from scratch and it’s running very well with avast! No problems on logon and loading programs.
It’s really hard to troubleshoot some seconds on delay in a particular system… Who knows what is going on… Although, maybe, some of the avast! programmers could take a look and post here if they have any solution. Sorry.