For this one I used two inline RegEx tools:
(\d:\d{2}.\w{2})
this slices out the stamp WITH the AM/PM.
I then used a Formula tool to convert the string into DateTime format so we can do calculations
DateTimeParse([Sunrise_time],"%I:%M %p")
the %p takes care of the AM/PM and
DateTimeDiff([Sunset_time],[Sunrise_time],"minutes")
takes care of the calculation of minutes, without necessitating complex logic to account for the 24-hour clock
Calculating the delta between the days seems a bit unintuitive, so I forced it with this inline IF:
iif([Row-1:Day Length (minutes)]-[Day Length (minutes)]>0,([Row-1:Day Length (minutes)]-[Day Length (minutes)])*-1,null())
I then used a Summary tool, Text Input tool and an Append Fields tool to mash up the last row to show the total difference over the whole month.
Overall it feels a little clumsy, especially the multi-row formula. But I approximated the solution (albeit I left mine with extraneous zero's or the seconds!)