Welcome to witching hour... or arsenic hour... or any other name you want to call it. Unfortunately, it doesn't just last an hour!!! For my two, it happened every afternoon from about 6 to 12 weeks. It was like someone hit a switch and all of a sudden they were unsettled. DP ended up changing rosters at work to be home by 4.30pm because it was too much trying to manage both unsettled babies at once.
Here is some info... http://www.breastfeeding.asn.au/bfinfo/fussy.html
It still happens now occasionally for us but no where near as bad. They're just tired at the end of the day and you know the end is near as you finish their feed, bath and then bed! Still, DP tries to be home by 5 to give me a hand incase things go haywire!