Why? What if the two ppl are living in different states and can't get rukhsatified at that time for school or whatever?
just ive seen way too many 'divorces' happening between the time of the nikkah and rukhsati hence i wouldnt recommend it.
I dont recommend long engagements either, but they are better than getting nikkahfied and then having to divorce when things go wrong. And we all know there is a very high risk of things happening