Method 1: Go to the business report in Seller Central.
Look at the days with decent sales volume, and analyze the hours where sales are generally higher.
For example, below are the sales statistics for a particular day. We can see the sales picking up around 6 am and slowing down at around 9 pm.
Method 2: Look at the Dayparting Trend report in Scale Insights.
This report will aggregate your sales across a few weeks/months and display the average sales for each hour.
For example, in the below picture, we can see that the sales are higher from 6 am to 9 pm.
Method 3: Use Scale Insights to create Dayparting Campaign (under Mass Campaigns).
It will create 24 Ad Groups in a campaign with the exact keywords and bids, enabling 1 Ad Group every hour and PPC statistics for every hour.
Identify the hours that are bringing you good performance.
Bonus Method
If you don't want to analyze, switch on your ads from 6 am to 10 pm as a general guideline.