Albert Barnes Commentary Acts 4:3

"And they laid hands on them, and put them in ward unto the morrow: for it was now eventide." — Acts 4:3 (ASV)

Put them in hold. That is, they took them into custody, or into safe keeping. Probably they committed them to the care of a guard.

Eventide. Evening. It was not convenient to assemble the council at night. This was, moreover, the time for the evening prayer or sacrifice, and it was not usual to assemble the Sanhedrin at that hour.