The Power Automate retry policy interval setting follow the ISO 8601 date format for durations. The ISO 8601 durations are expressed using following format, where (n) is replaced by the value for each of the date and time elements that follows the (n). P(n)Y(n)M(n)DT(n)H(n)M(n)S
P is the duration designator (for period) placed at the start of the duration representation. Y is the year designator that follows the value for the number of calendar years. M is the month designator that follows the value for the number of calendar months. W is the week designator that follows the value for the number of weeks. D is the day designator that follows the value for the number of calendar days. T is the time designator that precedes the time components of the representation. H is the hour designator that follows the value for the number of hours. M is the minute designator that follows the value for the number of minutes. S is the second designator that follows the value for the number of seconds.
“P3Y6M4DT12H30M5S” represents a duration of “three years, six months, four days, twelve hours, thirty minutes, and five seconds”
Date and time elements including their designator may be omitted if their value is zero, and lower-order elements may also be omitted for reduced precision. For example, “P23DT23H” and “P4Y” are both acceptable duration representations. However, at least one element must be present, thus “P” is not a valid representation for a duration of 0 seconds. “PT0S” or “P0D”, however, are both valid and represent the same duration.
To resolve ambiguity, “P1M” is a one-month duration and “PT1M” is a one-minute duration (note the time designator, T, that precedes the time value). The smallest value used may also have a decimal fraction, as in “P0.5Y” to indicate half a year. This decimal fraction may be specified with either a comma or a full stop, as in “P0,5Y” or “P0.5Y”. The standard does not prohibit date and time values in a duration representation from exceeding their “carry over points” except as noted below. Thus, “PT36H” could be used as well as “P1DT12H” for representing the same duration. But keep in mind that “PT36H” is not the same as “P1DT12H” when switching from or to Daylight saving time.
Alternatively, a format for duration based on combined date and time representations may be used by agreement between the communicating parties either in the basic format PYYYYMMDDThhmmss or in the extended format P[YYYY]-[MM]-[DD]T[hh]:[mm]:[ss]. For example, the first duration shown above would be “P0003-06-04T12:30:05”. However, individual date and time values cannot exceed their moduli (e.g. a value of 13 for the month or 25 for the hour would not be permissible).
Reference:
ISO 8601