I don't know if I'd support the additional features like auctioning off land claims and such mentioned in the follow-up reply, but I think the 1 in game year is a totally reasonable timeframe to use. Even with TOPS (or any other always running, 30 day month server) and 1 Game Year being 2 irl weeks, at a totally arbitrary 20 RG upkeep cost a full stack of 1,000RG lasts 50 cycles, or 100 irl weeks. And for another arbitrary amount, an upkeep cost of 100RG per 1GY would have a full stack of 1,000RG last 10 cycles or 20 irl weeks.
Pleeeeeenty of time to top up the stack, even with the super large upkeep cost. And that's just with arbitrarily large upkeep and player funds as examples, they'd both probably be much lower to be more realistic, but for those that do actually have a lot of RGs and want to claim a lot of land it would still be viable.