Yes, if you do it right. Generally, if sufficient pressure is applied to the carotids, your Brain will die within 20 min tops. Giving yourself at least an hour in case is smart. 2 is more than enough. There have been cases where not enough pressure was applied(usually due to the kneeling method) and they woke up hours later...although this isn't super common.
I hope you've exhausted your options if you've decided on suicide. I highly suggest taking your time and not rushing into anything. Feeling like this for a month is different than feeling this way for years. I'm not sure where you fall in that category, but just please be sure it's what you want.
We're here if you need to talk at all.
I wish you the best.