Bolt's very quick and keen on a regular basis (6)
I believe the answer is:
fasten
'bolt's' is the definition.
(thesaurus)
'very quick and keen on a regular basis' is the wordplay.
'very quick' becomes 'fast' (I've seen this before).
'and' means one lot of letters go next to another.
'on a regular basis' means one should take alternating letters.
The alternate letters of 'keen' are 'en'.
'fast'+'en'='FASTEN'
(Other definitions for fasten that I've seen before include "Fix securely" , "Fix to, secure" , "Shut" , "Attach" , "Tie, secure" .)