Hi @tannhq
This is because scheduled refreshes are put into a queue, whilst manual refreshes are run immediately.
Sheduling refreshes puts them on a queue to refresh, along with all other refreshes in the Power BI service you have a licence for. "On Demand" refreshes are at the head of this queue and are run sooner than scheduled refreshes. If you have a Free or Pro licence the scheduled refresh may be in a queue for up to 2 hours before timing out.
So the time you schedule refresh is the time it is put into the queue, which may include a wait until resources become available.
You can reduce to remove this wait by putting the content into a Premium Per User workspace, which has more resource capacity, or a Premium Capacity workspace, where you manage your own compute capacity to ensure each refresh gets the resources it needs.
see Data refresh in Power BI - Power BI | Microsoft Docs
Hope this helps
Stuart
