Hello @Pitawat
A lot of the documentation for things like Azure CLI, Rest API and PowerShell are generated via a script. In my experience, it's always best to look at the documentation for the product itself, not just the command line references.
With regards to your scheduled export issue, it is detailed here and has examples relating to your scenario. https://video2.skills-academy.com/en-us/azure/cost-management-billing/costs/tutorial-export-acm-data?tabs=azure-portal#export-schedule
"Scheduled exports get affected by the time and day of week of when you initially create the export. When you create a scheduled export, the export runs at the same frequency for each export that runs later. For example, the export runs during once each UTC day for a daily export of month-to-date costs export set at a daily frequency. Similarly for a weekly export, the export runs every week on the same UTC day as it is scheduled. Individual export runs can occur at different times throughout the day. So, avoid taking a firm dependency on the exact time of the export runs. Run timing depends on the active load present in Azure during a given UTC day. When an export run begins, your data should be available within 4 hours."
I hope this clarifies things
kind regards
Alistair