Query by date range - adding an additional criterion

Hello EE Experts,

I have a working formula that allows me to query a range of data by a selected date range.

=query(arrayformula(Helper!A3:N), "where B <= date '"&TEXT(N1,"yyyy-mm-dd")&"' AND B >= date '"&TEXT(L1,"yyyy-mm-dd")&"'") 

So, I can select a "from" date in cell L1 and "to" date in cell N1. This works really well, but it's inconvenient for the user if they want to see the entire dataset.

I'm trying to add in an additional clause to ignore the date range if cell O1 = "all"

But everything I tried results in a failure or nothing at all.

I created a mockup, please see tab "EEDateQuestion"

Note: This is using Google Sheets, but often an Excel solution is will work or can be easily adapted to Google Sheets. Thanks again. 

Thanks for your help.

https://docs.google.com/spreadsheets/d/1BolajiVLier4ov2ERdRcyAudJoj1zag5s94MBlGjeII/edit?usp=sharing