He was a Ph.D student between 1998 and 2002. If his vitae is trustworthy, he spent 4 years to get his Ph.D. Sounds fine.
However, he was in Fujian, not at Tsinghua in Beijing. Hence, it is impossible study normally.
We are people working in academy, and so we can make judgements by regular requirements of a Ph.D.
No matter what happened, Xi's Ph.D is a fake one. Or it is a fruit of power corruption in China.