Saturdays, Sundays and holidays shall be counted in computing the effective date of registration statements under section 8(a) of the act. In the case of statements which become effective on the twentieth day after filing, the twentieth day shall be deemed to begin at the expiration of nineteen periods of 24 hours each from 5:30 p.m. eastern standard time or eastern daylight-saving time, whichever is in effect at the principal office of the Commission on the date of filing.