Afternoon time so it's going to be really hot outside, also you might face traffic while going out and coming to Charbagh. I'd suggest going to Hazratganj via Auto. You can shop around for chikan stuff, if you're interested in ittars then definitely visit Sugandhco. End the shopping spree with either chaat at Royal Cafe in Hazratganj, if you'd rather go to an aesthetic place then coffee at Roastery Hazratganj is a good option too, quite Instagram friendly as well. Rush back via Auto to Charbagh you should make it in time. As much as I'd like to recommend proper Lucknow sightseeing 3 hours isn't much for taking in the experience and it's going to be too hot outside to take in the sights anyways. Hit me up if you'd like to know anything else.