8 seconds is the shortest travel time you can get, thats 4 flags @ 2 seconds per flag
And 2 round trips = 32 seconds
http://img42.imageshack.us/img42/5820/gjhl.png
so 10 minutes 32 seconds per cycle
10m32s = 632 seconds
Stadium Snack - 36 hours
36hrs x 60minutes x 60seconds = 129600 seconds duration
632/129600 = 205.06 cycles
205 (round down) x 25 beans = 5125 bean consumption (makes 4100 stalks)
a 5 flag travel time is 10m40s (640s)
640/129600 = 202.5 cycles
202 (round down) x 25 beans = 5050 bean consumption (4040 stalks)
6 flags is 5000 beans (4000 stalks)
etc etc
Know how many beans you need, and bounce the rest off a friend via mail so the buff and your beans run out at the same time. (Send the beans you won't be using to a friend for 1 fish, or 100,000 gold or whatever so they decline it, and it's in your mailbox)