35 weeks.. 3 cm dilated

Went to my check up today and was told I'm 3 centimeters dilated. My question is to mommy's that have already had their twins. How long did it take before you went into labor once you started to dilate? I have another appt on Monday and if there's a significant change my c section will be moved up and my babies will likely be born at 36 weeks.. which I'm also petrified over! I'm hoping my babies get to come home when I do but I know there's a chance they won't.