timers on shabbat

Question

dear rabbi, i've searched the Q&A regarding timers (shabbos clocks) and am still unsure about the following: [each question referes to a situation wherein the timer is connected to a light:] 1. if the light is on, can one take the pin out and place it back for an earlier time -- eg., if it is now 1pm and it is set to go off at 4pm, can one move the pin so that the light shuts off at 2pm? 2. if the light is on, can one push back the time for the ligh to go off later than originally set? 3. if the light is off, can one adjust the timer so that the light turns on earlier than originally set? 4. if the light is off, can one adjust the timer so that the light turns on later than originally set? thank you for clarifying.