Shortest?
Ten minutes I reckon.
I was 14 or 15 and my mother signed me up for strawberry picking.
Myself and two other lads from our street were driven to the farm by one of their mums.
When we arrived, we walked to the main gate. As we approached, the farmer was berating a couple of girls telling them they were too puny and weak so to go home.
He sized up the three of us and, indicating me, said I too didn't meet his standards so not to bother.
My mother seemed to think I had somehow punified myself just to spite her and give me a load of grief. This was undermined that evening when the other two lads came home, tired and filthy, having been worked to exhaustion and bilked out of nearly all their pay.
Next shortest:
An afternoon. It wasn't an actual job as such. I was on an employment course which was geared towards call centre work. We were nearing the end of the course so had a visit to a call centre which aimed to take us on as soon as we finished our course.
We stood and watched as this psychopath of a floor manager stomped about shouting abuse at her staff and threw fun-sized chocolate bars at them.
"Mary! Pick up that fucking call!" and then bounced a mini Mars bar off poor Mary's head.
The group of us decided that we wouldn't be applying for any call centre jobs.