To work this out required subtraction of the start time from the end time. Watching the clock on the wall usually means one has to count in steps of five. Furthermore, many people have problems with the fact that there are sixty minutes in one hour, i.e. time seems to progress in conflict with the metric system. Such issues appear too complex for many people. Newer VCRs tackle this problem by asking for both the start time and the end time of the program.
Some models allow for bar-code entry of program details.
The fact that it has taken so long for manufacturers of VCRs to come up with more friendly ways of time programming, is indicative for the established attitude towards maths. Maths is essentially a way to abbreviate words. Teachers did not like to write out long sentences on the blackboard. If sentences became too long, they did not fit on the blackboard and they became too hard too read anyway. So teachers started to introduce abbreviations and symbols.