Originally they accepted testimony regarding the new moon all day. Once the witnesses were delayed in arriving, and the Leviim blundered in the [daily] hymn. So they ordained that they accept [new moon testimony] only until the minchah; and that if witnesses come from the minchah onward, that day should be kept holy and the next day [should be kept] holy.  After the Temple was destroyed, Rabban Yochanan ben Zakkai instituted that they accept new moon testimony all day.  R’ Yehoshua ben Karchah said: This too did Rabban Yochanan ben Zakkai institute: that even if the head of the beis din should be in another place, the witnesses should go only to the place of the assembly.