You can set default opening and closing times to be used for all new items being added to online/mobile bidding at Site Settings > Online/Mobile > Bidding Settings.
Once created, items must be edited individually or in bulk to change the times (changing the default will not update existing items).
Contact Support if you want to set times in 5 minute increments (rather than 15).
To view and bulk edit times:
Go to Catalog > Online/Mobile Items > Select Items > Bulk Actions > Edit items: