Actually what you're attempting to store here, and what your users are entering, are simple string values, not time values as time values are understood by Access (8-byte floating point numbers).
You would need to write a little string parsing routine to locate the semi-colon in your string (e.g., Instr (1, "2:13", ":")), then parse off the characters strings to the right and left of the semi-colon, and append "mn." and "sec." respectively to the two sub-strings.
If I get some time I'll give it a whirl.