The enforcer will keep that nickname for 2 minutes, and the release it. However you can make NickServ release a nickname immediately by using the RELEASE command. The format is:
/NickServ RELEASE nickname password
NickServ will the remove the enforcer from that nickname and inform you that it is available for use.
If you need more help, please feel free to go to #DALnetHELP, where you can get help any time. If you'd like to obtain help by yourself type: /NickServ help.