Get value from another item and also schedule that newly created item

[Singularity]

I have item with type as zabbix-agent. It store value something like :
Main Item
Status : Completed
Start time : 2020-08-19 00:00:01
End time : 2020-08-19 02:32:14
Time taken (min) : 152.23

Scenario
1. I want to create an item which gets the Start Time value.
2. I also want to schedule that item.

Problem is:
1. if I use dependent item, then I cannot schedule it and
2. if I use calculated item, and in the formula I fetch last value of Main Item, I get an error cause calculated item expects numeric token.

How to create an item which fetches other item last value at scheduled time.

[cyber]

You can use that main item as a source for discovery. Each time main item receives new value, discovery is run again.