An interesting design challenge. The first thing that popped into my head is a sort of 'pulse'. An element that is showing how your cadence/flow is going.
Maybe it will move a little back when you are on a vacation, but you need vacations to keep building. But you are not losing the whole state.
Maybe it is even good to have a consistent pace, like every other day, or every weekend. Then it not the hours/days you put in that is the most important, but the progress you make over time.