Please find attached a workbook which demonstrates one way of achieving what you are after.
By changing the grain of the date (it's set to continuous minute) you can adjust the frequency that you are sampling for.
Hope this helps.
Time Frequency.twbx 131.6 KB
1) Choose how you are breaking out your days, by minutes, hours, half-hours, 15 minute intervals, etc.
2) Let's assume you chose hours as it is the easiest one and lets also assume this is retail sales so we assume a variance between days as well.
3) Right Click and drag your timestamp field to columns. When presented with a list of options choose 'hour' and make sure you select the one that is blue.
4) Right Click and drag your timestamp field to columns. When presented with a list of options choose 'weekday'
5) Using the drop down menu on your marks card change the default marks type to 'square'
5) Right Click and drag your SalesID to the colours shelf and choose CNT - This stands for COUNT
6) Click on the labels shelf of the marks card and select the option at the top (if you want), to show mark labels.
You've created highlight table where the darker colours represent a higher quantity of sales and the lighter shades a lesser quantity.