Welcome to the community, @Jason_Friedlander2! :grinning_face_with_big_eyes: A lookup field is most likely going to return an array, which is simply a container for multiple items. While lookup fields use commas to separate items collected from multiple linked records, those commas are purely for display, and can’t be used in formulas to distinguish where one item ends and another begins. While you could switch the lookup field to a rollup field to insert separators (using the ARRAYJOIN() function) to help with later parsing, that may or may not actually help depending on your data.
What exactly is the field being targeted by the lookup field? You referred to the data as “30 minute period 1 w/ Date” and “30 minute period 2 w/ Date,” but I’m not sure if these are just date fields or some other field type. The more you can describe about your base design, the easier it will be to help.
I think you’re referring to the technique that I describe in the video below to isolate the latest linked record, although you are looking for the earliest date instead of the latest date — so you will use MIN() instead of MAX().
This will work as long as you always link the 2 linked records in chronological order. The first date will always need to be linked before the 2nd date.
What type of data does the formula return? A string? A date? Again, the more info that you can share, the quicker we can get to a solution.
The technique mentioned by @ScottWorld will work if the formula field that you mention outputs an actual date (more accurately referred to as a datetime when referring to the data type itself). However, if it outputs a string, some extra steps will need to be added to the process.