The Chronivac is an absolute taskmaster and keeps you focused.
It's a machine with no empathy for your situation. The programming you devised yourself will will keep you prisoner until you ejaculate as a well-endowed male donkey. Just the thought of doing so sets your new equipment to tingling. It's the language of male hormones versus the cold logic of a machine.
Although you're now a different species, the sensations are all familiar. If anything, they're only growing more intense with every moment you remain in this smelly, gross, disgusting beast's form.
Your long, black hose of a cock hardens and sways beneath your sagging belly.
"Oh my god," you mean to utter. You only produce an unwelcome bray. "ErrrHaw! ErrHaw!"
That sound... that awful vocalization, brutish and strident.
Your brain sends out, almost like a reflex, a command for you to raise a hand and grip your cock. The command short-circuits before you can lift a foreleg and lose your balance. Your hands are gone, replaced by hooves. You have no fingers to encircle the cock and smoothly stroke it to that zenith moment that the Chronivac demands if it is to give you back your human form.
You hadn't had the forethought to recognize the disability of having no hands, only hooves. Insensate, blocky, useless hooves.
You grow panicky, which only fuels your erection.
You MUST ejaculate. Until you do, the Chronivac will enforce your imprisonment in donkey form.
How?
You're on a farm. Are there some convenient jenny donkeys?
Convenient? You groan. But that's why you programmed the stupid stipulation. To get back into your human form, you wanted to force yourself to experience a true humiliating low. You don't want to have sex with a disgust donkey jenny, but it's your only way back.