When setting sentence timestamps, the importer doesn’t like times which end in 0. For example, 00:50 will get converted to 00:5 and later this will show as 00: and the audio will not stop where it should.
Is that for Japanese? Unfortunately time stamp tool doesn’t work properly for certain languages and Japanese is one of them.
Well, generally it works fine, except when the seconds end in 0. I currently “fix” it by using for example 00:49 or 00:51 instead of 00:50. That doesn’t sound like it is related to any specific language, and in fact I have tried it with French and it works the same.
Actually, I have just found even better “solution”: Use 00:50.001 instead of 00:50 
Speaking of milliseconds, the importer also doesn’t like ending 0s in milliseconds… When I enter 00:50.100 it will save it as 00:50.1
Anyway, this is not a high priority for me as I can work around it for now…