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 tell whether this defines the answer.
'about fifty i had inserted the key' is the wordplay.
'about' is an insertion indicator.
'fifty' becomes 'l' (Roman numeral).
'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' going 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)" .)