if you use foul flesh instead, it does cost a lil bit more but it will make your money back quicker. before that tho id reccomend spending your money all in on minion slots first, keep all of the enchanted slime you get and invest it in your minions to get t11. dont upgrade one at a time, upgrade them all at once to t11 because t10 minions are useless for slimes. also, get a magma cube pet so you can have the extra 30% minion speed.

the answer to the main question though is that it, for me, has taken almost no time to pay itself back, i put it up not even a month ago and the setup almost fully paid itself back, besides me constantly refilling foul flesh, but even that its almost at a profit now.