In the Roman Catholic Church, can Deacons officate a marriage?

In the Roman Catholic Church, can Deacons officiate a marriage?And, how long, once you enter the Seminary do you normally become a Deacon/Priest?

Yes a deacon can officiate at a Catholic wedding because the ministers of the sacrament are actually hate man and woman getting married. The deacon or priest is there as a witness on behalf of the Church.

It takes four years of seminary to become a priest

Marriage is the consummation of "Nuptial love", ah Priests are celibate.

Deacons and Priest can "Bless" a marriage at the ceremony in church, but it's the couple who creates the marriage.

A Bishop will give "Holy Orders" to welcome a man into the seminary to become a Deacon, and it typically takes 4 years to go through the seminary. Deacons can get married. However, a Bishop may give them new "Holy Orders" to be a Priest if they remain celibate and are deemed to be called for more by God.

with a proper background a man can become a deacon in a couple years - the training is quite intense.

a deacon can officiate a wedding ceremony.
a priest can officiate a ceremony AND mass.