This should be achievable if you create a condition and flip it to advanced mode. In the advanced mode, you can use the same expression syntax that Logic Apps uses. Expression reference is here: https://msdn.microsoft.com/en-us/library/mt643789.aspx
From there, it depends on the exact date format stored in Excel. If it's the usual ISO format (or similar), it will start like 2016-05-13 (i.e. year-month-day). If you just need an exact date match, other formats could work, but if you want to detect "earlier than" it will need to be a string sortable format (i.e. year before month before day).
So, start by using the editor to do a basic comparison with the timestamp field, then switch to the advanced view. This will tell you how to reference the field you care about in the expression. I my example I chose to use a 'Created' time from the flow trigger when testing this.
Then, to do the actual comparison, we can trim just the date part from the timestamp, and compare it against a custom-formatted utcnow expression. So putting this into the advanced condition did the trick for me to test if the date was today: @equals(substring(triggerBody()['Created'], 0, 10),utcnow('yyyy-MM-dd'))
If you need to check for previous dates instead, this should work: @less(substring(triggerBody()['Created'], 0, 10),utcnow('yyyy-MM-dd'))
