It's a side project, you're not supposed to have a deadline. Though sometimes a deadline makes "completion" more of a certainty, if you want to complete a side

It's a side project, you're not supposed to have a deadline. Though sometimes a deadline makes "completion" more of a certainty, if you want to complete a side project you may need to push the milestones to a conclusion in some unfamiliar way other than the well-known corporate deadline. And completion may look very much different, you may end up with less of an MVP and more of an incredibly useful product. So you work on it anyway, even without a clear goal all the time, you want to make progress regardless dont you? Something good will come up in ways that will not happen if you halt.