Just after Thursday I will be very busy (2,3,2)
I believe the answer is:
on the go
'very busy' is the definition.
(I've seen this before)
'just after thursday i' is the wordplay.
'just after' becomes 'on'.
'thursday' becomes 'th' ('Th' can be a synonym of 'thursday').
'i' becomes 'ego' (I've seen this before).
'on'+'th'+'ego'='ON THE GO'
'will be' is the link.
(Other definitions for on the go that I've seen before include "Very active (colloq.)" , "Busy and active" , "Running around busily" , "Keeping busy, not stopping" , "Moving -- active" .)