How to calculate worst hour and best hour of the day by Visits and show them as separate columns?

I don't believe you can display data natively in Workspace as you are trying to do.... 

You can create a "heatmap" showing on average the best and worst times of the day, based on day of the week (I will show that at the end); and you can get the "Max" and "Min" value for the column, but this will just get you the value of the day with the most/least visits, and will show that value on every row (to get by hour, your table would have to have each hour on the row - really not what you want to show).

If I were trying to create such a report, I would probably use Report Builder to pull the data in with an hourly granularity, then use Excel Formulas to find the min/max value (all doing this in "hidden tabs") and stitch the final data together into the final requested format in a visible tab.

What I do know how to do, and I know this isn't exactly what you want... but, I would create a freeform table using the Visits metric, but broken down by "Day of Week":

Then use "Hour of Day" in the breakdown:

Then I would configure the Visits to be "conditional formatting"

Then finally turn off the values:

This will create a "heat map" of your traffic high/lows for whatever time frame you select:

So it's not the high and low for each specific day, but creates a nice visual of your traffic times for quick consumption (not so colour blind friendly if that is a concern... it would be nice if we could configure 'high", "low" and "mid" range colours.... )