Auto merge ?

What you're describing sounds like a rolling merge.

A rolling merge is a merge action that groups older layers into time periods (days, weeks, months, years) and, as the layers age, automatically merges those groups into single layers.

In your example, a rolling merge something like

Keep most recent: 9 months
   Followed by:
        0 day layers
        0 week layers
        0 fortnight layers
        12 month layers
        1 year layer

would do approximately what you're asking. When you run this rolling merge action, any layers within the past 9 months would be preserved. Layers in groups of months, going back 12 more months, would be merged into single layers (one layer per month). Any layers in the pervious whole year would be merged into a single layer, and then anything before that would be merged into its own layer.

So if you ran this today (January 2020), the merge would:

Leave whatever layers you'd captured since April 1, 2019 untouched (that's the "keep" part)

Merge all layers in March, 2019 into a single layer
Merge all layers in February 2019 into a single layer
Merge all layers in January 2019 into a single layer
....
Merge all layers in June 2018 into a single layer
Merge all layers in April 2018 into a single layer

Merge all layers between April 2017 and March 2018 into a single layer

Merge all layers before April 2017 into a single layer

The beauty of the rolling merge is that it "rolls." You can run this action twice a day if you want, but it would only do something if there were multiple layers within a group. For this action, it wouldn't do anything more until you ran it again in February.

When this action runs again in February 2020, now there are a group of layers in April 2019 that get merged into a single layer. And when it's run in October of 2020, all of the single-month layers between January 2018 and December 2018 now fall in the year tear and get merged together.

The new rolling merge action editor has a really cool (if I don't say so myself) animation that will let you preview the effect of the rolling merge as you edit it.

And there's always QRecall Help > Guide > Actions > Layers > Rolling Merge.

Post again if you have any more questions.