On the list of scheduled listings, there should be a link in the dropdown menu to revise them - I'm not sure if you can do this in bulk, or whether it has to be done manually one at a time, but I have done it myself manually several times, so this if for the manually, one-by-one way...
Once you have selected revise, scroll down to the scheduled start time, either untick the box for the scheduled time so the the listing will go back to immediate, ore edit the scheduled time so that it's for tonight, then scroll down to the end and submit. The next screen will be the review page, then submit again and your changes will be saved.
