The dates in HTTP headers are GMT (may explain the 1 hour difference). If Booster finds an "Expires: " http header it checks to see if is a past date. If the expiry date is in the past, then it uses the current time plus 1 second as the expiry date. If the expiry date is valid and in the future, then it just uses that value.
If this is not working for you, can you:
a) check to se if the time on the booster server is correct
b) send me the http headers that domino is outputting so we can verify here that all is working as it should.
send to bupson -at- wnc.net.au