Some cursory math tells me there's somewhere around 11-13 learning days' worth of skills available in Glitch. Now, for Better Learning V to save you enough time that it "pays" for what it cost, you'd need to learn 14-15 days' worth of skills (that's before we worry about cutting 20% off). So, accounting for the fact that my math is pretty rough, we can say it might be worth it if you learned all the Better Learning skills before learning anything else.
This seems wrong, though, so if somebody could double-check my math and/or leave a comment, that'd be great.
My math was as follows:
Better Learning V takes about 2 days, 20 hours (according to my skills page) to learn. For it to "pay" for itself, 20% of all the subsequent skills you learn must be greater than 2 days, 20 hours (68 hours), meaning that you'd need to learn 14.2 days' worth of skills after getting Better Learning V for the 20% cut to justify spending the initial 68 hour investment. Rough totalling leads me to believe that that's about how much the total time is for ALL the skills is. More generally,
payoff_time = learning_time / learning_time_cut
Here,
payoff_time = 68 hours / 20% = 340 hours.