A question from my N5 mock test book reads:
A 「何{なん}時{じ}に うちへ 帰{かえ}りますか。」
B 「７時{じ} ( ) 帰{かえ}ります。」
１ ごろ ２ じゅう ３ まで ４ ぐらい
The answer was 1, but I've been taught that both ごろ and ぐらい are interchangeable when talking about points in time (時刻), like 7時 or ４月.
Is ぐらい really acceptable when ごろ should be used?
(Note: I am of the impression that ぐらい and くらい mean the same, and so do ごろ and ころ.)
A 「[何時]{なんじ} に うちへ 帰 {かえ} りますか。」
B 「７時 {じ} ( ) 帰 {かえ} ります。」
１ ごろ ２ じゅう ３ まで ４ ぐらい
The only possible answer is 1) ごろ.
Had the fourth choice been 「ぐらいに」 instead of just 「ぐらい」, it would also have been a correct answer. Not sure where you have been taught it was correct to say 「～時ぐらい帰る」, because it is not.
So, to say "to return home around 7-ish", you can use:
「ごろ」, 「ごろに」 and 「ぐらいに」.
But you cannot use 「ぐらい」. In other words, 「～時ごろ」 can function adverbially to modify the verb 「帰る」 without a 「に」. 「～時ぐらい」 cannot; It needs a 「に」 to function adverbially.
The following usage of 「ぐらい」, however, is correct.
A 「家に帰るの、いつも何時ぐらい？」
B 「７時ぐらい。」
This is OK because there is no verb following in either line. You don't need an adverbial phrase here.
