The tours are offered every 45mins (i think) until like 4:30 or 4:45 (sometime after 4pm but before 5pm, I know that).
You can book "on the hour" tours in advance by calling 407-WDW-TOUR. This may be helpful in that the tour is seemingly very popular and limitted on space - I think 12 guests is the max, 10 is ideal.
I went on the tour both before and after it's "refurbishment" that happened while the pavilion was closed for the Soarin' installation.
They've made a concious effort for the tour to be more family friendly, as it was a little dry in the original version. The activities they added however aren't just fun for kids, but interesting for adults willing to be a little childish too
You get the tour of the greenhouses, good bug production, and things of that sort. You get to start growing a pocket garden, and depending on the season you may get to try/eat/get seeds from something. I've never come out of the tour with the same exact "stuff" at the end.
Once my tour guide was there doing an internship on entemology (if i spelled that right - the study of bugs) and thus we spent a lot of time in the bug labs. Another was a girl working on cross breeding and hybrids so we focused on the plants that fell into that category a bit, but both tours were well rounded.
I think it's worth it, a steal at the 10-12 that it costs per person, and even mroe worth it if you qualify for any of the discounts.
The tour, btw, is called Behind the Seeds.