Using auto-play with mortar monsters, this is what I got:
| Levels | 1-10 | 11-20 | 21-30 | 31-40 | 41-50 | 51-60 | 61-70 | 71-80 | Total |
|---|---|---|---|---|---|---|---|---|---|
| Average time (s) | 32 | 43 | 57 | 71 | 119 | 134 | 157 | 196 | 2hrs 40mins |
With the fact you have time between the battles and will not efficiently end/start new battles while using auto-play I found that in practice it’s about 3hrs per SE to lvl 80.
There’s about 270 SEs in the game right now so that’s roughly 800 hours of auto-play. I’ve done it over the course of a little under 2 years.
I go into greater depth in this thread: KD's HP Boost guide (in the second post, in a dropdown at the end of it). Please note the Purpie team I refer to for manual play is outdated, since that strategy doesn’t work properly any more.