Depends on whether your intent is to win them all or not. If so, either:
Place your one TRUE maximum bid on each at your leisure in the days, hours, or minutes leading up to the endtime. There are advantages to waiting as late as reasonable (keeps your options open, limits the time other bidders--or a dishonest seller using another account--have to probe your hidden maximum to bid just over--or worse just under--your maximum bid amount) .
OR
Use a "sniping service" to place your bids (again, your TRUE maximum that you are willing and able to pay for the item as listed; without regard for what anyone else appears or doesn't appear to be bidding) in the last few seconds to take full advantage of the advantages of later bidding described above.
IF NOT (if you only want to win one--or some) then either:
Choose which one(s) you want to win well ahead of time and place your TRUE maximum bids on each as the end approaches (substituting another one from your list if the minimum bid amount on an auction goes over your TRUE maximum before you submit the bid (but not if it goes over AFTER you submit the bid as you could still win even though you were outbid during the auction if the higher bid is cancelled before the auction ends and you are required to pay if you do). The rest you just do without bidding on.
OR, if the auctions do not end at the EXACT same time:
Check out the "bid group" function (might be called something else) of the sniping service where it will submit your bids in turn until you win one (or for some more flexible ones, a number you set) auction and then stops submitting bids. Each service will set its own minimum time between the auction endings where this will or won't work; if they end too close together you will have to pick which one(s) to set up bids on and set those up and do without bidding on the others.
