Convert formatted text to fixed text value (time)

I have a report where I use four character time values from a manual text field in our database, for example a field may have been entered 1345 (i.e. 1:45 pm) and excel just registers it as a general/number field. There are a handful of these for each encounter to which I have various formulas and algorithms to compare elapsed time between indicators. There is one timestamp in the database that I also compare to these numbers, however the timestamp is standard excel date/time system, e.g. 13:50:00 PM or 0.576388888888889 as the Excel timevalue. I cant use this in my formulas against the other four character values cause it isn't an apples to apples value, e.g. 0.576388888888889-1345=-1344.42361111111 when I really want 1350-1345=5

Currently, I custom format the timestamp field to hhmm, then copy and paste it into minitab which strips any backend formatting and then I copy it back into excel and it is in the fixed hhmm format I want with no excel timevalue in the backend.

Is there a a way to dynamically do this in excel so I dont have to do the minitab roundabout?