Distances travelled about two days in former times (6,4)
I believe the answer is:
middle ages
'former times' is the definition.
(I've seen this before)
'distances travelled about two days' is the wordplay.
'distances travelled' becomes 'mileages'.
'about' is an insertion indicator.
'two' says to double the letters.
'days' becomes 'd'.
'd' duplicated is 'dd'.
'mileages' going around 'dd' is 'MIDDLE AGES'.
'in' is the link.
(Other definitions for middle ages that I've seen before include "Historical period" , "historic period" , "some time in the past" , "former times" , "way back" .)