The phrase "It's time somebody did something..." is a common one and whilst I can see why you might expect it to be in the present tense, it's actually correctly written.
The phrase "Assuming he keeps his job till then..." is an example of the present simple being used to express the future, by the way.
"It is time..." refers to the present.
"...he did something useful" as I said is a common expression.
The writer is saying that the time has arrived for the subject to do something useful. I would assume that he has been in his position for quite a long time and has not done anything useful yet.
It's time you went to bed.
It's time he got married.
It's time they drank all that wine.
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