American trips taking in crumbling hall on an irregular basis (2,3,5)
I believe the answer is:
at all hours
'an irregular basis' is the definition.
I know nothing about this answer so I cannot tell whether this works.
'american trips taking in crumbling hall' is the wordplay.
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'trips' becomes 'tours' (I've seen this before).
'taking in' is an insertion indicator.
'crumbling' indicates an anagram.
'hall' is an anagram of 'allh'.
'tours' going around 'allh' is 'tallhours'.
'a'+'tallhours'='AT ALL HOURS'
'on' acts as a link.
Can you help me to learn more?
(Another definition for at all hours that I've seen is " At irregular times of day".)