I see there is no answer here, so, hopefully this helps you out if you don't already know.
To me, a charge cycle doesn't have such a rigid definition, whether you charge from 20% to 100% or 50% to 100%, each one I would call a charge cycle. But, it depends, because there are some deep cycle lead acids that may not define a charge cycle the way others do, and vice versa. So, I would consult who ever the manufacturer is and see what they say.
Basic/typical lead acid charge cycle looks like the image below
Image Source: Research Gate -
Paper Name: "Solar Charger Sizing"
Disregard the numbers, just see the terms "Bulk", "Absorption", and "Float".
Bulk is constant current, meant to be your high (Constant) current (relative obviously) portion of the charge cycle, to get you most of the way there (usually around 80% or so) to your target voltage depending on the type of lead acid.
The absorption phase finishes the rest of the 20%'ish (can overcharge relative to your final resting voltage), and, essentially allows the battery to cool down and vent gasses as a result from the Bulk stage. I just found this website and it gives some indication as how to calculate how long the absorption portion of the charge cycle should be (https://www.ecosoch.com/charging-lead-acids-properly/). Hopefully you find that interesting.
Because lead acids relative to li-ion self discharge more, float charging part of the cycle is meant to compensate this intrinsic issue. The current at this point naturally decays, and, once it hits a certain value the charger turns off.
Hopefully this helps!