It is really your decision as to how long increments should be, and therefore what the elapsed time should be as the number of increments can be approximately derived from the time the check would take if no increments were involved and dividing by increment length. I say approximately as any other disk activity going on at the same time as a check can slow it down thus potentially increasing the number of increments.
I see you are using the ‘custom’ option to get the increment schedule you want rather than the default of daily.. Would you see any good reason to add other repeat intervals to avoid using the ‘custom’ option? I had avoided doing this as I wanted to keep the GUI simple and daily seemed what the vast majority of users would want. I then and added the ‘custom’ option to cater for special needs (and it helps me with testing).
The check will not reset to 0 as the plugin does not start the parity check itself, but merely pauses and resumes one started by the system.
I am not sure what the behaviour will be if both pause and start time are identical as it will depend on exactly the order the pause and resume get executed as to whether a check is left running or paused. I think I will add a check to the GUI that the Pause and Resume times are not identical as it could mean that behaviour is unpredictable, and I cannot think offhand of a Use Case where it makes sense (but you are welcome to suggest one).
I am not sure I tested this but it should be treated as a manual check because it was not initiated by a cron entry. I will add a check for that to my test checklist though to make sure it is.
For reference Automatic checks are the sort that are started automatically by the system after an unclean shutdown is detected and if any other type of check gets flagged as Automatic this is a bug in the plugin that would need investigating and correcting.