need help on a trigger

hihi, i need help with a trigger that do the following

when the gametime = 18 o'clock, the unit type of footman will start losing 1 life every 10 second if his mana is = to 0.

can anyone help me do this please?

uhh

every 10 seconds

time of day = 18:00

pick all units of type footman matching matching unit's mana == 0 mana
set unit property [life] (picked unit) to unit property [life] - 1


going to need to make it time of day between x and x, like 18:00 and 20:00