Is it healthy to snack in the evening? How long before bed?

Not always. I have a general rule (often broken when there's ice cream in the house) to not snack past 8pm. Almost everything we eat past 8pm is unhealthy - unless you make a good effort and have some fruit or something. When you eat too close to bed, you also worry about reflux during the night, so make sure to eat at least 2-3 hours before going to bed.