You need to use appropriate time informats when reading the data so SAS converts the source strings to SAS time values. This allows you to then use these values for calculations.
You also need to apply the appropriate time formats so when printing the values they become human readable.
data demo;
input arrival_time :time. departure_time :time.;
format arrival_time departure_time travel_time hhmm5.;
travel_time=departure_time-arrival_time;
datalines;
16:05 20:55
04:05 20:55
;
proc print data=demo;
run;
If you don't understand yet how SAS Date, DateTime and Time values work then read the following:
https://go.documentation.sas.com/?docsetId=lrcon&docsetTarget=p1wj0wt2ebe2a0n1lv4lem9hdc0v.htm&docse...