Petroglyph

Can I please have a detailed explanation as to exactly what the petroglyph will do and how it works? I cannot tell if there is a glitch in the system or it is working as expected?

I can see a reduction in research time when I add tasks, and if I add more tasks the time reduces more. But as soon as the tasks are completed the time reverts back as if the tasks were not "ordered".

If it makes things clearer, it generates additional science points while the task is active.

This is the timeline for my use of petroglyph in Simba II:
Learning progress during building task:
12:45 pm: 2 days 2 hours
2:25 pm: 1 day 21 hours

Petroglyph building task ends
Learning progress at 3:00 pm: 2 days 0 hours

This is the timeline for my use of petroglyph in Simba II:
Learning progress during building task:
12:45 pm: 2 days 2 hours
2:25 pm: 1 day 21 hours

Petroglyph building task ends
Learning progress at 3:00 pm: 2 days 0 hours

At 6:00 pm I got back down to 1 day 21 hours. So in order for me to keep the progress gained from the task, I must keep it going for the entire learning process?

This is the timeline for my use of petroglyph in Simba II:
Learning progress during building task:
12:45 pm: 2 days 2 hours
2:25 pm: 1 day 21 hours

Petroglyph building task ends
Learning progress at 3:00 pm: 2 days 0 hours

At 6:00 pm I got back down to 1 day 21 hours. So in order for me to keep the progress gained from the task, I must keep it going for the entire learning process?

I've noticed the same thing.  It is murder on your stone stockpiles.

I have another question about the petroglyph.

My tasks at levels 1 to 4 offer 650 points for 50 stone over a period of 48 minutes. At level 5 it offers 1000 points for 100 stone over a period of 2 hours (120 minutes). Logic says that if I order two of the lower tasks it costs me 100 stone - the same as the one of the more advanced tasks, however yields 1300 points over a period of 96 minutes. What is the advantage of choosing the more advanced task?