Typically about two hours. However, the longest part of it is the emptying of inbox, wallet, voice mailbox, etc. What I consider to be the most valuable part, the review of projects, someday/maybe and the capture of new open loops is only about 30 minutes.
If I skip a week or two, the weekly review takes about 4 hours and I have to split it over two days. This has given me motivation to stay current.