With these time expressions we are thinking about a definite or finished time in the past, so we wound normally use a past tense. Compare the following: When did Brenda phone? ~ Not long ago.

We do sometimes omit on in time expressions in informal English, although I think it is more characteristic of American English than British English. So in your first example, Anid, both versions ...

They proposed that tense expression deficiencies could result from two separate processes: encoding and retrieval. During encoding, a speaker develops the idea of time. During retrieval ...

By: Amit Goldenberg, Jonas Schöne, Zi Huang, Timothy D. Sweeny, Desmond C. Ong, Timothy Brady, Maria M. Robinson, David Levari, Jamil Zaki and James J. Gross ...