Let the torpor drain to 10% and pump it with a ton of narcotic to extend amount of time you can leave.

Knocking it out is the easy part. Keeping it down? Better have a few hundred narcs

A level 25 has 2k torpor and loses about 8torpor per second

How to tame a therizino is getting on a tall rock and then use darts and then when knocked out bring lots of bio toxic and narcotics and lots of berries (this is how I tamed a therizino and it was level 2)