"It is just a matter of time."

Translation: To tylko kwestia czasu.

[mcpk]

'To jest tylko sprawa czasu' is suggested as a correct answer, but 'to tylko sprawa czasu' is marked incorrect - why is that?

[Jellei]

That looks like an oversight, however... we've agreed that 'sprawa czasu' is strangely unidiomatic, I really can't imagine hearing that. So I'm going to delete this answer.