Short answer, any day of the week that was a Sunday or other Holy day. There was also the provision for private baptism at home at any time.This was to ensure a sickly baby was baptised .Many parish clerks note whether the baptism was private and also, if the baby survived when it was admitted to public worship. ( but this is rarely noted on indexes )In the earlier period it most likely occurred at the earliest opportunity after birth(by the 19th c, some families delayed for years)
Note that during the civil war and the Commonwealth (under Cromwell) many babies were not baptised .An extra service to cater for those not baptised as babies was introduced in the 1662 book of common prayer.