Does anyone speak about doing this BEFORE one goes to bed?
Is that allowed?
While tikkun chatzos should preferable be said at chatzos (midnight), however if it is difficult for one to do so, the Shulchan Aruch Horav (Siddur) writes that one can start from the beginning of the middle third of the night, which would be two hours before chatzos. (Shaos zmanios, are not 60 minute, clock hours, but calculated by dividing the nighttime into 12 equal parts, with each one being an hour. In the winter, when the nights are longer each hour will be longer than 60 minutes, and in the summer they will be shorter than 60 minutes.) In the winter time it could be about 9:30 – 10 p,m., however in the summer it would be later, bet. 10-11 pm.