As a general rule of thumb...after placing in flower, Indica doms will double (or slightly more) in size, Sativa's can tripple or quadruple in size. I kiddingly refer to it as P.M.S. (pre-motherhood stretch) It depends a lot on pot size, and when you last transplanted. (or when you plan on the final transplant) I usually transplant into final pot within a week and a half or two weeks after going 12/12. (sometimes a tad sooner) The flowering ladies appreciate the fresh soil and footroom.

Tiz up to you about the reverting back to veg, but it does take extra time for the plant to revert. Not bad if a normally stable strain like WW, but if growing bagseed or strains with sketchy genetic stability, this can stress 'em too much. Unless you are looking for 5 foot monsters, you might want to keep on keepin' on in flower.

What size pot(s) are you in? When did you last transplant?