Unless I’ve missed something, cleanups occur between 3 and 5 AM with now way to configure. I run incremental backups for a number of remote (Internet) desktop PCs (Mozy-ish) and would far rather do cleanups during office hours and backups at night.
The cleanup window should be configurable. See http://www.urbackup.org/administration_manual.html#x1-480008.1.9