Having counted to about fifty, I had inserted the key (6)
I believe the answer is:
relied
'having counted' is the definition.
I can't judge whether this defines the answer.
'about fifty i had inserted the key' is the wordplay.
'about' is an insertion indicator.
'fifty' becomes 'l' ('L' can be a synonym of 'fifty').
'had' says to put letters next to each other.
'inserted the key' becomes 'reed' (I can't explain this - if you can you should give a lot more credence to this answer).
'l'+'i'='li'
'li' placed into 'reed' is 'RELIED'.
'to' is the link.
Can you help me to learn more?
(Other definitions for relied that I've seen before include "Trusted confidently, depended on" , "Assembled as before" , "Had confidence" , "Depended on or fibbed again" , "Was dependent (on)" .)