Route reserve is the contignency fuel. You can set either mass or a % of the trip fuel. Once airborne, this fuel is added to the extra fuel.
ATLN/TIME: The figure below ALTN is the amount of fuel required to the alternate. If hard tuned, as it is in this case with 1.2 tons, no time is displayed. If you leave the ALTN blank, the FMGS will calculate the amount of fuel required to your alternate and the flight time. For the best prediction you enter the alternate routing in the flightplan.
FINAL/TIME: figure below final is the final reserve fuel, time is the amount of minutes.
When you divert depends on the situation. You can either use all the extra fuel until you arrive at your min dest fob. At that point you would have to divert. You can of course also divert before touching your extra fuel.
If you start touching your final reserve fuel you become a fuel emergency.