You could create a variable and store your calculated dates in there. This variable can then be used in your xpath.
You could set up your variable like this:
addDays( '[%BeginOfCurrentDay%]' , -1)
This would result in the begin of yesterday.
I would create a DateTime before the retrieve activity, to define the end of tomorrow, using the expression: addDays([%EndOfCurrentDay%],1)
[BaguetteType='Kylling'
and
BestiltDato >= '[%EndOfCurrentDay%]'
and
BestiltDato >= $EndOfNextDay]
Or you can use in xpah this:
BestiltDato >= '[%BeginOfCurrentDay%] - 1 * [%DayLength%]']
more here: https://docs.mendix.com/refguide/xpath-keywords-and-system-variables/