My son was homeless and made multiple requests to the probation officer and probation dept. to obtain a transfer to California from Nevada. Turned out this probation officer lied and said no contact attempts were ever made. He was arrested on a bench warrant in May 2017 and still no evidenciary hearing some six months later? Now they scheduled the evidenciary hearing in December 2017... can they just hold him indefinitely? No time limits here?

They can hold him normally up to the time on his sentence.
If his requests were not in writing, with proof they were made, they were never "made" officially. And requests for transfers do not have to be made. If they can not show proof of a job and proof of housing in the new location, they are seldom allowed