According to the International System of Units (SI), the abbreviation of seconds is s. Neither sec, secs, sg or any other should be used (even if Wikipedia says you can use sec).
It is not permissible to use abbreviations for unit symbols or unit names, such as sec (for either s or second), sq. mm (for either mm2 or square millimetre), cc (for either cm3 or cubic centimetre), or mps (for either m/s or metre per second). The use of the correct symbols for SI units, and for units in general, as listed in earlier chapters of this Brochure, is mandatory. In this way ambiguities and misunderstandings in the values of quantities are avoided.
You can download the SI brochure here
PS: same thing for hrs in the case you find it. It's just h.