The higher your level. So you can do Survival Trial at the beginning of the day, stop when you get stuck, level up, and complete that trial at your higher level. Every trial, as you unlock them, scales to your level, so if you stop at 11, level up, then complete 11, the trial 12 you unlock will be harder, I believe.

Pretty obviously they are not givng you lvl 10s as a level 70

No survival trail if u reset it on same lvl as u been u get normal oppenets to ur lvl and power, difficult incrasing if u getting more power and more lvls

Yea the player levels get higher during survival. Not exactly the power. Power is more important imo. If you stay on top of power, no matter what level you get in survial, you should be able to clear it. Honestly I can say that I never had a time where I couldnt clear the full trial. Not including the practice trials where I might or might not do them depending on rewards

^What Hanzo said

The only caveat I'd say to that is to always do Trial Breakthrough if you have the time and/or you have the characters to challenge it. It still gives you Cultivations Runes and starting lvl 70 and up (and probably before then), runes become harder and harder to keep up for your teams.

It doesn't help that you're always getting new and better characters that replace your team. (All those cultivations runes used on Neji and now we have GNW Neji...)

Opponents levels become higher, the higher level you are.