is it possible to make it as a day trip from Guangzu?

Do you mean the day trip from Guangzhou to Guilin? If yes, I think it is quite rush to do it in one day. The high speed train between two cities takes around 2.5 hours and you will arrive in Guilin at 10:30am if you take the first train. The last bullet train leaves from Guilin at 20:44. I am afraid that you can only take a short city tour in Guilin during this period. As for the Li River cruise, it is available at 9am and 9:30am, so you can not catch it upon arrival. Therefore, you are suggested to arrive at Guilin one day early if you want to take the cruise. Or you may consider taking overnight train to GL and catch the cruise in the morning.