Nevertheless, a variable element begins to take time (3)
I believe the answer is:
yet
'nevertheless' is the definition.
(I know that nevertheless can be written as yet)
'a variable element begins to take time' is the wordplay.
'a variable' becomes 'y' (algebra).
'begins to' says to take the initial letters (I've seen 'beginning to' mean this).
'take' is a charade indicator (letters next to each other).
'time' becomes 't' (abbreviation).
The first letter of 'element' is 'e'.
'y'+'e'+'t'='YET'
(Other definitions for yet that I've seen before include "Still, so far" , "Although" , "Still; however" , "Still; nevertheless" , "'But, however (3)'" .)