The census was held on a Sunday either that last weekend in March or the beginning of April. Sunday night when most people would be at home.
You'll notice the first census in 1841 was held in June and not successful at all, because the bright sparks in the city who organised it, didn't realise, it was during the agricultural season and most people were away for the harvest. The 1841 census in England and Wales was the first census where the names of all the occupants of the household were taken.
They were administered in census districts which were based on the registration districts used in the civil registration of births, deaths and marriages. These districts were made into divisions of about 200 households called enumeration districts and enumerators were employed ( yes! they were paid)to visit the households and explain the forms, much the same as they do today.
The districts did not always match the existing parish boundaries.
The date of the census were:
Sunday 6 June 1841
Sunday 30 March 1851
Sunday 7 April 1861
Sunday 2 April 1871
Sunday 3 April 1881
Sunday 5 April 1891
Sunday 31 March 1901
Sunday 2 April 1911
Census returns are subject to a 100 years' privacy rule
I couldn't resist adding this History of the British Empire from Horrible Histories.
Special forms were supplied for asylums, hospitals, schools and similar institutions
with over 100 occupants.
The form below is the 1911 Census