ぐらい・ごろ
About, approximately (quantity: ぐらい, point in time: ごろ)machine translation
FormationQuantity + ぐらい / point in time + ごろ
Both mean "about," but they're used differently: ぐらい (or くらい) goes with QUANTITIES — durations, numbers of people, amounts of money: 十分ぐらい (about 10 minutes), 二十人ぐらい (about 20 people). ごろ goes with POINTS IN TIME: 七時ごろ (around 7 o'clock).
A tip for telling them apart: if it answers "how much, how long" → ぐらい; if it answers "at what time, when" → ごろ. Compare: 一時間ぐらい寝ます (sleep about 1 hour) with 一時ごろ寝ます (go to bed around 1 o'clock).
ぐらい and くらい are interchangeable, with no difference in meaning.
Examples
駅まで十分ぐらいかかります。
It takes about 10 minutes to get to the station.
毎晩七時ごろ家に帰ります。
I go home around 7 every evening.
パーティーに二十人ぐらい来ました。
About 20 people came to the party.