Technically there are not really any restrictions until either the holder of ILR or until applying for naturalisation.
Holders of an ILR will lose it completely if they are out of UK for 2 years continuous
The only other time residency restrictions are counted is when applying for UK naturalisation.
For those eligible under the 3 year residency rules (those married to a British Citizen and holding ILR) they will need to have been:-
- in the UK on the date three years prior to the date the application is received in the Home Office and
- had no more than 270 days of absence from UK during the three year qualifying period and
- had no more than 90 days of absence from UK during the last 12 months of the three year qualifying period.