[OSM-newbies] Tagging opening_hours from public holiday to public holiday

[Bill & Kathy Patterson]

I'm attempting to correctly tag the opening hours of an ice cream parlour, which is open from noon to 20:00 seven days per week, but only during the summer.  To complicate matters, it doesn't open and close on specific dates, but opens for Canada's Victoria Day weekend (Victoria Day being the Monday on or preceding May 24th, but the opening would be the Saturday 2 days earlier) and remains open through Canda's Thanksgiving Day, which is the 2nd Monday of October.
Currently I've used "opening_hours=Mo-Su 12:00-20:00; May PH-Can_Thanksgiving", but is there a better way of capturing that particular range of summer dates?