Just for the record, numbers in that format (nnn:nn) will not translate well because the standard Access date/time functions don't recognize hhh:nn (or nnn:ss) as a valid format. If Access can't write something in that format, the odds are pretty good it can't read that format either.
You can try to write a function that would convert the STRING "136:30" into 136.5 as a number of hours, but by itself, 136:30 is neither a valid time nor a valid number. You can search this forum for articles on custom time conversions and find several hits, I'm sure, because I remember seeing some. Just none that were recent.