OK, i found the cause for the services starting late.
At home i use a wired cable connection to internet.
I'm currently staying at my in-laws' because i'm having renovations done, where i go online through a wireless router.
My wired internet connection at home has a dynamic ip-address.
The avast services (and some others) wait for the network adapter to get an ip-address, which takes a long time, since it's not connected.
If i disable the unconnected adapters, or give them a fixed ip, the avast services are running when i reach my desktop.
Except for the mailservice, which has to wait for a start command by the mailprovider i guess.
I'll have to check wether e-mails get scanned now when retreived immediately after logon.
edit:
ok, that was it.
Apparently my adapter used for internet connection (Dlink DE-520) does not report a cable disconnected, which causes the dhcp client to try and get an address, which of course times out, keeping a bunch of services waiting.
This may be fixed by using the dlink drivers, instead of the windows xp included one.