I was doing some searching with Ask Jeeves today and noticed that that cached pages that Jeeves includes in its database now include the date and time (to the second) the page was last cached by the AJ crawler. Look for it in the box at the top of cached pages.
Although I'm not 100% sure if this is a new feature (I'll check), I haven't noticed it before.
AJ began offering cached versions of some content in late 2004.
Here's a quick review of what some other engines offer in terms of date and time info with cached pages.
+ Google also offers both a time and date stamp on cached pages.
+ MSN Search provides a date stamp but doesn't include a specific time.
+ Yahoo does not offer either a date or time stamp but does provide a direct link to The Wayback Machine for the specific cached page you're viewing.
+ Gigablast offers a date stamp at the top of cached page and a direct link to The Wayback Machine as part of each snippet.
Postscript: I also noticed that date and time info is also visible with pages from the Ask Jeeves UK cache and other Ask sites like Ask Spain.