has anyone ever requested an interview date change/delay?

If I have an interview date scheduled for March for an Immigrant Visa at the US Embassy in Bogota, and I request a delay in the interview date, will I be able to request a interview date in the month of June instead?

The interview in question is for Follow to Join visas for the minor children listed on their mother's original K-1 visa.

that visa was issued in July 2007.

we understand we must receive the Follow to Join visas before the one year anniversary date of the original K-1 visa issued in July 2007.

She is now married and living in the US and going thru her own AOS application having already received her work permit and travel permission while continuing to wait for her green card.

bottom line, we want to delay the interview in Bogota until the month of June and then have an additional 6 months to prepare for the children to Follow to Join.

By then, the children's mother should have received her green card and finished her cosmetolegy school.

however, we are afraid if we do not accept the March interview date, we will not be granted a new interview date before the July cutoff and be required to reapply for an entire new application for the children.