Summit of Twitter these days following Apple regularly (4)
I believe the answer is:
apex
'summit' is the definition.
(I've seen this before)
'twitter these days following apple regularly' is the wordplay.
'twitter these days' becomes 'x' (I can't justify this - if you can you should believe this answer much more).
'following' is a charade indicator (letters next to each other).
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
The alternate letters of 'apple' are 'ape'.
'x' after 'ape' is 'APEX'.
'of' acts as a link.
Can you help me to learn more?
(Other definitions for apex that I've seen before include "Summit - pinnacle" , "climax" , "Apogee, summit" , "Summit or peak" , "reasonable fare" .)