It’s not unusual for seed to germinate at different times, even a few days apart as you have witnessed. In my experience, this is especially the case for plants with larger seeds, such as the cucumber plant.
Cucumber is traditionally a spring planted summer crop. In my experience growing vegetables in both temperate and subtropical gardens, all cucumber seeds prefer heat and lengthening days to germinate consistently and the plants prefer very hot weather to grow and fruit vigorously.
Cucumber plants can be grown anywhere at any time of year, but to do so requires a lot more effort, care and specialist equipment, such as a mechanically ventilated greenhouse.
I’d recommend you leave your cucumber plants in the ground, but do not expect vigorous growth or fruiting until the days become longer and the weather warms up.
Note that extremely cold weather and frosts will ultimately kill your plants. You can take some steps to protect your plants. One example that may work in your climate is covering the growing bed in a “half-pipe” tube made from bent sticks/poles and clear plastic.
However, I’d recommend you choose another two or three varieties of vegetable that are better suited to growing through the cooler months. They may even provide some shelter and help protect the cucumber plants.