Welcome to the community, @Rob_Crawford! :grinning_face_with_big_eyes: This can be done by forcing the check in and check out dates to effectively crop out the time, then taking the diff from those. In my test, I made a pair of formula fields. Here’s the one that strips out the time from the {Check In}
field:
IF({Check In}, DATETIME_PARSE(DATETIME_FORMAT({Check In}, "L"), "L"))
This formats the date and then parses the result using the same date-only pattern. Technically this doesn’t really remove the date because the date is still stored internally. It just resets it to midnight on both days, which effectively gives DATETIME_DIFF()
an apples-to-apples comparison. Just replace “Check In” with “Check Out” to get the other formula.
If you would prefer everything in a single formula, here you go:
IF(
AND({Check In}, {Check Out}),
DATETIME_DIFF(
DATETIME_PARSE(DATETIME_FORMAT({Check Out}, "L"), "L"),
DATETIME_PARSE(DATETIME_FORMAT({Check In}, "L"), "L"),
"days"
)
)