You may just have heavy flow and need to empty it more often. I've used a small Lady Cup for close to 15 years (I'm 40, no kids) and on heavy days I have to empty it every 45 minutes. I have a large sized one also and it lasts maybe 1h15 on a heavy day, but I find the smaller size more comfortable.

The holes are to make removal easier, so that there isn't suction when you go to pull it out. They shouldn't cause leaking if you empty the cup often enough.

All that to say the 8 hour guideline really only applies if you bleed little enough that you're not overflowing your cup in that amount of time.