Many people do 1-day trips to Wuzhen, from Hangzhou, Suzhou or Shanghai. Going there early in the morning and come back in the evening. Personally I think it's best to visit for 2 days.
I've done a day trip and two 2-day trips to Wuzhen, and personally prefer to stay the night there. Wuzhen may not be big, but it has two separate scenic areas called Dongzha (East Quarter) and Xizha (West Quarter). While the sceneries are similar during the day, Xizha is bustling at night and you can only enjoy it if you spend the night
The ideal itinerary for Wuzhen is to get there by lunch time on day 1, spend the rest of the day visiting Dongzha (which is smaller than Xizha). Make your way to Xizha in the late afternoon and spend the night there. On day two tour Xizha in the morning and afternoon, then go back to Hangzhou/Shanghai/Suzhou
Keep in mind that it takes 2-3 hours to get to Wuzhen from Hangzhou/Shanghai/Suzhou so day trips are very tiring