One way they could slow the whole process down is by convincing Pelosi to call for a house vote. If that were to happen, they would have a bunch of chances to slow the vote down.
As soon as the house investigation is over, I expect them to switch again. The GOP will want the trial to happen ASAP and the dems will be dragging their feet.
It doesn't matter what they do, the dems are painted into a corner. There is no winning move for them. If they impeach, Republicans can bring their own evidence via subpoenas devastating the dems. If they don't impeach, they piss off their base. If they continue with this impeachment theater they piss everyone off.