No, there's no scheduling tool for Lemmy, or else I probably would, honestly.

I just try to make at least one post at day. If I come across more than one interesting thing or have some time to paw through my sources, I try to remember to come back in two or so hours to post it as well.

Generally my posts cluster around a few sources for a stretch of time - for the past two weeks I've been relying on 4 sites for artifacts, for example, and I think all of my posts have been from one of the four. Eventually I'll move on to some other sources and do the same with them for a few weeks.