TLH (Total Listening Hours) is a rolling total. It only reflects the listening hours a station has accrued in the last 30 days. If you had more listeners 31 days ago than you had yesterday, then your TLH will be less than it was yesterday.
Your US-TLH on the Dashboard, which is weighted against your package total, is based on your anniversary renewal date. For example, if you signed up on Feb 2nd, your US-TLH is counted from that date.