I did a search and found some sites say "drink w/in 24 hours".
Others say "w/in a few days, before the juice turns brown".
I have never had mine turn any color other that yellow.
I wonder if juicing the whole lemon (with little bits of peel in it) helps preserve it better than just the juice on the inside (juicing by hand).
Lemons have been used for years for cleaning so I don't think their enzymes are fragile (like an apple).
Congrats on completing the fast.
I hope you are feeling "healthier" than before.
I'll probably go another month, my tongue is still white.