144h twov. I'll spend 3 months in Shanghai from September to November due to my study exchange.

I'll have a visa with one entry to China. After finishing my studies I'm planning to travel to Japan, South Korea or Hong Kong for a week. I still haven't made exact travel plans or chosen the destination. I have a return ticket from Helsinki to Shanghai ( Sept - December) so is it possible to return for example from Tokyo to Shanghai 3 days prior my return flight to Helsinki and stay there with 144 hours twov as my visa has only one entry to China?