That look reasonable to me. The RTC module will not be super accurate but good enough for this I would think.
Do I need anything else?
How are you going to set the time? That will probably have to be done in the field as the RTC creeps over time. This normally requires an LCD and some buttons which is a pain if that's all they are needed for.
An alternative is to have a single button that forces the time to a given value, say 6PM. So every few days/weeks or whatever you press the button at 6 o'clock.
There will be some mechanical linkages to get as well. If this is outside a good enclosure will be required.
Rob