I've been freelancing remotely for the past six years. Here are some of the things I've learned over the years.
Since I've been mostly working for US-based startups I am constantly under pressure to have a big overlap with their time zone. It's easy to relent under such pressure and effectively switch time zones.
I've been working for a year in a San Francisco time zone, starting my day at 5 pm and going to sleep at 3am. It's not healthy and I would not recommend it to anyone. It's just not worth it, don't do it.
If you feel that this is not a project that matches your interests or skills, don't be afraid to ditch it and search for a better project or client. There's always a better and worse client than your current one. It might take some time and luck to find a better match, but time spent searching for better matches is definitely worth it.
Knowing your boundaries is a key for a healthy relationship with your client. Saying no takes character, but it makes your client respect you more. Know when to say no in order to prevent yourself from being spread too thin.
Saying no to some things allows you to say yes to other things. Say yes to things that matter.
Knowing when your work day starts and when it ends is key to having a healthy work-life balance. Be strict with yourself. This is one of the biggest problems with freelancing - you're your own boss when it comes to deciding if the work day is over or not. Be a good boss to yourself and set the working hours strictly.
Routine stuff like daily standups help since they are always happening at the same time. I currently have one standup at 10am, so I usually start my working day with it.