Do they really need two days for synchronization? This delay is something I'd like gone from Adsense.
I may be being too suspicious but maybe Google has to do a more thorough check on the source click IPs with channels. If there are several websites with their own channel designation under one account then maybe G checks for multiple click thrus from the same IP but via different web sites/channels under the same account to double check against any fraud and this may account for the extra time needed.