Time flux

https://preview.redd.it/zit9pr46jjph1.png?width=1622&format=png&auto=webp&s=828b707541c9c98d1f24f14ad2bcf961edb793fd

My next upgrade costs roughly 95 hours to gain 0,0116m/h (25% boost from shop), so it would take around 8142h until it pays off (considering i never let my time flux full), which is almost a full year offline. It makes sense to upgrade if i don't use time flux that much, but i'm at attack 635 and time flux is starting to become very useful. Should i keep upgrading it? Is there a ceiling? And the TF gain decreases after every purchase, which means the next one is gonna take even more time to pay off.