I see that the TimeTree of Life project is now public.  This collaborative project draws on the research of dozens of biologists to estimate the timing of past evolutionary divergences.  The work is available as a book, but the online version has an interactive section that allows the user to name two organisms and get back the date the two last shared an ancestor.

For instance,

Ants vs. Bees: 163.5 million years ago

A word of caution, though.  While the output is extremely precise (i.e., it gives exact dates with decimal places), precision is not necessarily accuracy.  The given dates are really the midpoints across a range of estimates, and for appropriate scientific caution you’re still best off consulting the referenced papers themselves. In our insect example, the work was done by the Smithsonian Institution’s Seán Brady.

Still, it’s a fun little tool.