Code:
on !*:join:#:{
$+(.timerpoints.,#,.,$nick) 0 900 add.pts $+(#,.,$nick)
add.pts $+(#,.,$nick)
}

This is an event triggered when someone enters your chat room. It contains 2 lines.

Line 1: The first thing this on join event does is create a timer named points.#channel.$nick. This timer trigger infinite times (designated by the 0) every 900 seconds. It triggers the add.pts alias. It passes one word to this alias #channel.$nick.

Line 2: The second thing this on join event does is trigger the add.pts alias. It passes one word to this alias #channel.$nick.

If you do not want users to gain 1 point when they join the channel, instead, only when the timer elapses: Which line from the 'on join' event do you need to remove?