What if I place an order that is split into two, prompting me to pick up items on two different days? I have an order to pick up on Monday and another on Wednesday. Do I have to pick up the first one by Mon. or can I wait till Wed. to pick up both?

You can wait till Wednesday to pick up both.

Just adding more to the other answers, when Amazon emails you that a delivery is ready, they will tell you how long they'll hold it at a particular delivery location.

U can wait. They will hold the first package for about a week (I believe longer- not sure exactly how many days but at least a week) and all packages will be in one locker when you pick them up

Yes, as long as you retrieve your packages within two weeks of their arrival date.

You can wait and pick both together.

Wait to pick up both orders at the same time

You can leave packages for several days, so you can definitely wait 2 days and get them both at the same time. They'll send reminders if you forget about a package.