a couple comments.
1. The :#: should be modified to list the name of your channel, so it doesn't activate in #help or every other channel you're in.
2. The user should understand this isn't going to greet 100%. The %j is an anti-flood method to avoid yourself flooding if many people join at the same time, but it also means that if 2 ops join at the same time, only 1 gets greeted.
3. This should not be forcing the timer to be named after the nick. It risks replacing a legitimate timer like timerDaily or timerHourly if someone happens to join with that nick. If someone knows what scripts you're running, and knows if one of them depends on a timer that repeats after long intervals, they can use this to disable your script. Either maliciously or for the lolz.