Thanks for your patience.
I discussed with Product team and they confirmed that the tumbling window trigger starts at window end time (For daily pipeline it is 2020-09-21 00:00:00) and it adds offset (1 day) to it and pipeline actually runs at 2020-09-22 00:00:00.
The same is replicated when I have used hourly and 5minute triggers. In this case, hourly is dependent on 5minute trigger with an offset of 5minutes and the delay of 5min after window time is seen in triggering time of hourly trigger.
Hope this clarifies the query. Please let us know for further queries and we will be glad to assist.