If the timer is in the fan, it may not be possible to disable the timer without disabling the fan itself. Based on the labels (L,T,N), I would guess that L is the switched input for the light and T is a switched input that starts the timer for the fan. You can test this by disconnecting the T terminal (make sure you cap the bare wire before turning the breaker back on) and see if the fan still functions with the switch.
If it doesn't, you're probably looking at altering the internal wiring of the fan to bypass the timer (not something I would recommend or consider safe). If this does turn out to be the case, I would take the covers off of the fan if possible to see if there is a timer duration adjustment in the fan someplace. You may just be able to turn it down to zero (or a considerably shorter duration).
That said, it sounds like you are trying to disable a feature of the fan that is there to ensure that the fan is on long enough to remove moisture from the bathroom. The reason fans are equipped with timers is so you can leave them running long enough to work without having to go back later and turn them off (and/or having to leave the lights on while they are running). I would ask myself if the reason you are trying to disable it is worth running a risk of issues with mildew and the host of other problems that can stem from inadequate ventilation. If it's a noise issue you might think about just replacing the fan with one that is quieter.