User blog comment:SpiritedDreaming/RWBY: Attack on Kevin Tower Defense Game/@comment-26397825-20161011121047/@comment-28288412-20161011215521

A new suggested idea in this chain Hazel is daily spawns (depending on the Grimm type) which are less in number but add up to the weekly total.

So creeps daily, 15hp every two daya, etc (read Spirit's second reply in this chain.