Skin Care serum

I just bought a vitamin c serum and it contains salicylic acid, hyaluronic acid, niacinamide, retinol, and msm. I know retinol is suppose to be used during the night but the directions on Amazon said I could use it day or night. I think I should probably just use it at night. Let me know what y’all think. But I do have a question because I just read that niacinamide shouldn’t be mixed with vitamin c and that vitamin c shouldn’t be mixed with retinol.. it has over 51,000 reviews and 4.5 stars, so now I’m at a crossroads. If y’all have any professional information I’d greatly appreciate it💜