"I only got off work at 11 last night."
time phrase in a Chinese sentences can be in 1. position or second position: Wo zuotian wanshang is correct, but so is Zuotian wanshang...
I've been wondering about it for some time now and most of the time I've chosen the other place that Duolingo does not accept...
In this sentence it does the job of the English "only", which could also be "not until" as in "I didn't get off work until 11 last night." So you can't use it everywhere you can use "only" in English.
But is there an implied meaning of past? I mean here it's obvious because of the time indication at the start, but otherwise? In another exercise there was no time indication, no 了or 完, yet the correct answer was in past tense.
才 (CAI2) should be used when an action occurs later than expected. For example, 我昨天晚上十二点才回家 (I didn't return home until 12:00 last night).
The opposite of 才 is 就 (JIU4) and should be used when the action occurs earlier than expected. For example, 我昨天晚上七点半就回家 (I already returned home by 7:30 last night).