Unless the tests set forth in both paragraphs (a)(1) and (2) of this section are met, cash remuneration for service not in the course of the employer's trade or business is excluded from wages. (For provisions relating to the exclusion from wages of remuneration paid in any medium other than cash for services not in the course of the employer's trade or business, see § 31.3401(a)(11) -1.)
An employee who on a particular day reports for work and, at the direction of his employer, holds himself in readiness to perform service not in the course of the employer's trade or business shall be considered to be engaged in the actual performance of such service on that day. For purposes of this exception, a day is a continuous period of 24 hours commencing at midnight and ending at midnight.
26 C.F.R. §31.3401(a)(4)-1