In most cases yes. The only strain I have grown that showed sex in less than two days after the photoperiod switch was an auto blue mammoth by Barney's Farm. The ruderalis did not kick in until I switched photoperiod to 12/12.
The males can display first and can show within 3-5 days. I have found females to take a bit longer but have always been able to tell by day 7 at the outside. Good luck, it's hard killing the male babies after taking such good care of them!