There are several CL products FDA approved for sleeping in them for a week to 30 days. So you dont have to feel like you're doing something wrong. I'd still recommend trying this out at home before you do it in the field. Some eyes cant tolerate it very long even if the FDA is okay with it.I store them on my eyes, then use about 1/4 bottle of solution to lubricate everything in the morning. Shouldn't do it but have never had good luck putting in and taking out contacts camping, hard to get clean hands for that type of thing camping.
This is what I did last week and it worked perfect. Keep your bottle of solution in your bag also.As others have said, keep them on your body or in your bag at night. Saline should freeze at lower temps than plain water, but i see you're from Minnesota, you're probably talking about a magnitude of cold i'm not familiar with.