"Get undressed! It's time for your bath!"
Translation:Раздевайся! Пора мыться!
Hm. Given the translation, it is a possibility. «Купаться» means you are not there to wash.
If you want the answer Раздевайся! Пора мыться!, the English text should be "Get undressed! It's time to bathe!" Otherwise I answer Раздевайся! Пора твоя ванна! and you should accept it.
Sometimes the DL rules are very sticky about details, like using past imperfect to translate an imperfective verb in the past tense. Sometimes they require a free translation when a literal one would do. Not the best thing for users trying to learn at a basic to intermediate level.
Пора твоя ванна is ungrammatical, in about the same fashion as "It is high time your meal". Пора in that meaning attaches verbs, even though you might use something else in the English translation.
- actually, it also attaches adverbial phrases of direction (e.g., "Ну всё, пора на работу"). If what you mean is "It is time for someone to go somewhere" you can omit the verb of motion in Russian.
I changed the translation back to "for you to bathe". The one you saw is in fact what an English speaker came up with.
You can use время (somewhat) but that is at times a bit dramatic. "Время для ванны" just sounds disinterested and bookish. "Пришло/Настало время для ванны" is about as colloquial as "The time has come for you to bathe".
In short expressions with verbs время is OK. For example, Moscow has a few diners that are called Время есть (a pun on the two meanings of есть)