'gurai' vs 'goro'
Hi again. According to my lessons, 'goro' is used for time, as in

'hachi-gatsu goro made'

and 'gurai' for anything else, as

'nijuu meetoru gurai massugu itte kudasai'

but then in another lesson they just use 'gurai' for time, as in

'[osaka made] nijuugo-fun gurai desu'

or

'sannen gurai made tokyo ni sundeimasu'

so... are they just used randomly or something? haha. Thanks in advance for any help! You don't even know how useful italki has been with clearing doubts :)

Question

'gurai' vs 'goro'
Hi again. According to my lessons, 'goro' is used for time, as in

'hachi-gatsu goro made'

and 'gurai' for anything else, as

'nijuu meetoru gurai massugu itte kudasai'

but then in another lesson they just use 'gurai' for time, as in

'[osaka made] nijuugo-fun gurai desu'

or

'sannen gurai made tokyo ni sundeimasu'

so... are they just used randomly or something? haha. Thanks in advance for any help! You don't even know how useful italki has been with clearing doubts :)

Answer

ぐらい is used to express an approximate duration or quantity of something
ごろ is used to mark an approximate point in time

Ex:  あの電話は三十ドルぐらいいかかります。 Ano denwa wa sanjuu doru gurai ikakarimasu.  That phone costs about thirty dollars.

五分ぐらいバスを待っていました。
Go fun gurai basu o matte imashita. I was waiting for the bus for about 5 minutes.

この本はペエジが百二十まいぐらいあります。
Kono hon wa peeiji ga hyaku-ni-juu mai gurai arimasu.
This book has about 120 pages.

バスは五時ごろ（に）来ました。  Basu wa goji goro(ni) kimashita.  The bus came around 5 o'clock.

(With, "goro," "ni," is optional)

Again, "gurai," is used to mark an approximate duration or quantity, while "goro," is used to mark an approximate point in time.  "Goro," can only be used with a point in time, while "gurai," can be used with a quantity/cost or over a span of time.