I just brewed a 11 gallon batch of Pale Ale on Saturday. Split it into two 6 gal carboys. One went into fermentation chamber (converted freezer) and one into fermentation closet. Exact same ingredients, same Nottingham yeast. The one in the closet started in a few hours and is still chugging along. The one in the freezer just started Monday night. Both are kept at 68, but I think the closet is more constant. Bottom line is, yes, sometimes there will be serious lag times, but I've never seen one not start.