This is not good.
20 seconds is not the norm.
You still haven't explained what else you do in your sessions.
It all depends on what i can use, the gym is not very busy but is quite limited in what it has.
Only has dumbbells up to 25kg.
This is what i done today..
I start with running on the treadmill, get the blood going, 10 pull ups or however many i can do, then go down to the weights room, BP 50kg warm up - 15kg either side + 20kg bar. 8 reps, that't not really heavy for me, so i consider it ok for a warm up. 2 sets of those. 10 pull ups, then back on the BP, 20kg either side now and 20kg bar, 8 reps, 10 pull ups, then 8 reps and no more pull ups.
30 kg either side and 20 kg bar, 6-8 reps, 7th and 8th rep are really pushing it, only done 3 sets today as i just couldn't do anymore.
Moving onto dumbbells, 10kg bells, lying down on bench to work chest, did as many as i could, think it was around 25.
done the same but moved to 12kg bells, done 20, moved up to 15kg and done 15 then final set moved up to 20kg and managed 10.
same routine as above to work arms in seated position.
Then just spent around 20 minutes on random machines doing back and stomach.
Finished on the cross trainer for 25 minutes.
I am probably doing everything wrong, but i will never learn what's working for me if i don't try my own ideas.