abbreviation of units of measure: 'hours' vs. 'minutes'

Solution 1:

What you have shown are common abbreviations: whether they are standard abbreviations depends on what you mean by standard. Officially, in this context, standard refers to abbreviations that have been officially set out by a national or international body.

I suspect you are wrong in stating that hrs is 'standard' for hours, while min is standard for minute(s). It probably depends who wrote it. I would say that all of the following are commonly used abbreviations:

hour(s): h, hr, hrs
minute(s): m, min, mins

Solution 2:

Standard units of measure have standard abbreviations. The hour and minute are not standard units (the standard unit is the second, symbol s), and consequently their abbreviations are not entirely standardised.

Note that where hour is used as a unit, for example in kilowatt-hour, it does have a standard symbol, h. The symbol for kilowatt-hour is kWh.

Note too that there is a difference between symbol (which is standardised) and abbreviation (which is not).