Yes, but I would not recommend it, especially given the short time you have.
Singaporeans frequently go on a day-trip to Johor Bahru (or "JB" as they simply call it), which is just across the Causeway (the bridge linking the two countries) to the north of Singapore. Sometimes they even go slightly further afield for a day trip. So yes it is perfectly feasible.
Food. Singaporeans and Malaysians like to argue over whose food is better. IMHO, the food in both places is superb and has fantastic variety; and to the Westerner visiting only briefly, it will be indistinguishable.
Shopping. Shopping in Singapore is better, if more expensive. Singaporeans do cross the border to do their shopping, but mostly to get quotidian stuff (like chewing gum which cannot be sold in Singapore).
Culture and feel. Malaysia definitely has a different feel from Singapore. But like many cities in Malaysia, Johor Bahru has a large Chinese population (close to a majority). Moreover, JB is amongst the richest cities in Malaysia (though still visibly poorer than Singapore). So while it is certainly different from Singapore, it is less different than you might imagine.
You land at Changi at 2:30pm. Best case scenario: Clearing immigration + collecting your luggage takes only 30 minutes; taking a taxi to the border is another 30 minutes; clearing immigration there and getting into JB proper is another 30 minutes. So best case scenario you're in JB at 4pm. So you have late afternoon and evening in JB. Then you have to get back to Changi no later than 8:30am the next day. So altogether it just doesn't seem to be worthwhile. It'll just be exhausting running about for a low return. Better to just stay in Singapore.