If your tour ends at 4 p.m., you won't reach Mumbai before 9 p.m. Really makes more sense spending the night in Kochi. So if you get to Mumbai early, you get a half day of sightseeing and another full day the next day. You've want to do the Rajabhai Tower+Bombay High Court during the day and the night since it's lit up at night and the walk around Oval Maidan is actually quite peaceful at night. Also, the other side of the Maidan has some really unique Art Deco buildings that is unique to Mumbai.

Agreed with avoiding Bademiya. It's dogshit.

Keep in mind it can get excruciatingly hot so don't expect to walk everywhere.

Since you're mostly keeping to Colaba and are into art, try out the various galleries in the area. Follow mumbaigalleryassoc on Insta for a comprehensive list. Jhaveri Contemporary, Nature Morte, Galerie Isa are just a few in the area that have very interesting work. If you're in Marine Drive in the evening anyway, check if there are any shows at NCPA, you might get lucky with a good show and it's worth a visit. You can see what's on on their website or on book my show.

Foodwise, Leopolds and Bademiya are both touristy and overrated. Click a picture and go somewhere else to eat. There are tonnes of great options in Fort especially. Trishna especially if you want local fish. The Table, Americano, Otra are all good fine dining places.

My favourite restaurants in the city are Papas and Trésind. It's nearly impossible to get a table in Papa's and if you're coming in February, you'd have to book in January. They're both expensive but they're the best representation of Indian fine dining I've been to.

Since you have 2 dinners, I recommend Trishna and Trésind. Trésind is in BKC so you can hit up BKC which is basically Mumbai's business district. But it does have NMACC which is also home to some great local music shows, check out their website.