From MyHeritage for Canada Day. I can't see the end time, but they usually say 11:59p.m. Mountain Time, which I make to be 7:59a.m. BST on Wednesday 3rd.
IntroductionCatalogueFrom Ancestry.com, a huge number of histories and directories of churches, schools, employers, etc. Until 10:00a.m. ET = 3p.m. BST Tuesday.
IntroductionCatalogueYou need accounts (free) but don't have to sign up for free trial of the whole sites. No payment details are taken on registration.
As always with free periods, save anything you find on your own device, as you'll need a sub to see it after the offer closes.
I am told that some of these records are always free on the above sites or elsewhere, so check before you spend all your time on one particular set.
Whilst I'm here, Ancestry also has a new always free collection of
Slavery-related newspaper articles.