You could use a /timer, but /ban has this functionality built in:

Code:
ban -u<time in seconds> channel type address


Eg:

Code:
//ban -u900 #channel 2 somenickname


If you want to kickban someone:

Code:
ban -ku<time in seconds> channel type nick reason


Eg:

Code:
//ban -ku900 #channel 2 somenickname You just got kickbanned for 15 minutes :o)

New username: hixxy