Example.

Making up dates

Book a trip from New York to Chicago on Airline ABC

Monday Feb 18 fly New York to Chicago on ABC
Friday Feb 29 fly Chicago to New York on ABC

That includes a Saturday night stay

Book Chicago to New York on Airline XYZ
Friday Feb 22 fly Chicago to New York on XYZ
Monday Feb 25 fly New York to Chicago on XYZ

Then you will use them this way

On the 18th fly out on the first half of the Airline ABC Ticket
and return on the 22nd with the first half of the XYZ ticket

On Monday the 25th fly out with the second half of the XYZ ticket, and return on Friday the 29th on the second half of the ABC ticket

You need to use two separate airlines, as you are combining tickets to not have to meet the saturday night stay requirement, and the airlines contract of carriage prevents you from doing that. You have to use up your tickets before using part of a next one to keep you from doing this.

I don't know the bump probabilities on that route (for some reason I hardly ever fly it during heavy times anymore), but that's another way to keep the costs down overall, if you can predict the good chance of getting a bump flight, and use the vouchers for a later trip. When I was getting bumped a lot on that route, there were always later flights that evening to get me home (Boston at the time), so it was like being paid cash, and it was cash at the time and a free ticket) to sit in a lounge for a couple hours.