The answer is quite simple... hrs.
Quite simple but quite incorrect - in three ways in three letters
1) the international convention is that units are expressed in the singular - no s at the end - that would make it hr and not hrs
2) the international convention is that two letters are not used if one is unambiguous - that would make it h and not hr
3) the unit is defined by the BIPM (guardian of the SI units recognized everywhere but the rogue regimes of North Korea and the USA) as h
every four hours
T1.5 = Time @ 1.5 hours
24/7 sounds like 24 7
Hours can be abbreviated using the degree symbol. Minutes can be abbreviated using the single quote (apostrophe).
The abbreviation of "have not" is "haven't."
h for hours, m for minutes.
pm
pm
Hours (divisions of time)
The abbreviation for hour would be hr.
hrs and mins, respectively.
every four hours
T1.5 = Time @ 1.5 hours
The medical abbreviation for every four hours is q4h.q4h
24/7 sounds like 24 7
In construction it means " Machine Usage Ratio " . It is the ratio of no. of hours for which machine worked to no. of hours for which machine was available.
The correct abbrevation for the word hours is HH. Which means A duration of time expressed in hours. Which was quite odd, that's something a lot of Americans are unaware of.