DMNFTF — Errors in date/time arithmetic

In 10.3.2.11, Table 41 (beta-3), in the row for date-time + year month duration, the operation definition adds seconds to months.

In the same table, in the row for time +/- day time duration, it is easily possible to get a result that is not in the value space of time [0s, 86400s], and it is not clear what inverse value-sub-t returns.

In table 41, the description of date time +/- years and months duration is corrected.
In 10.3.2.3.4, constrain the inverse of value\t to [0, 86400], by taking the operand modulo 86400.