spells can be cast day or night, some people perfer casting at night because they're using the power of the moon, or to set a mood. unless the spell requires the suns energy, you can cast it whenever. if i were you though i would cast during the waning moon as this is the time to cast spells to send things away, starting on the full moon. [so cast it three nights in a row]
the love spell should be cast on the opposite cycle, during the waxing moon as the moon is growing full and pulls things towards you. potions are basically liquid spells, so you could drink a tea with herbs like lavender, cinnamon and/or catnip, or you could mix these together in a bath, then soak in the water, or you could use this as a perfume. whatever you choose, be sure to charge with energy, and visualize.
without more specific information it's hard to say exactly what you need, but i'm guessing someone stole your boyfriend and you want them to suffer then for your boyfriend to get back together with you. [or something along those lines] you will probably learn the hard way, using magick for these reasons will result in bad things, but if you must, you could try this Break up Candle Spell i wrote, basically it combines two spells that are rather effective. i would wait for a few days until the half moon, in that time, i suggest you think and decide if it's right to cast. be careful what you wish for, and be aware spells can and do backfire.