Unlike historic CNC machine languages like the one used on the Fanuc NC Controllers, which used the following time format values for G04 (Dwell):
LinuxCNC and Buildbotics, which are free and open-source firmware and open-source hardware CNC controllers respectively, follow the RS274NGC standard which defines a P word for G4 and assumes its value to be in seconds. It accepts a floating-point number.
On MASSO G3, a proprietary closed-source universal CNC controller, which uses its own proprietary g-code dialect, the value of P is interpreted as milliseconds.