Yes, you can absolutely move the timings up so you can go to bed at midnight. I've sometimes changed it so that I can go to bed at 2am - and it's worked fine for me!
I don't know why your Epsom Salts don't taste bad. They don't taste like salt at all...but they taste bitter. And yours? My ES don't have a brand...maybe someone in the US can point you in the right direction.
I'm sure the lemon will work just as well - it'll just be quite sour!
I'm glad to see you're taking it all slowly and gradually....