There's no requirement to have been resident in UK for any specific period.
You may be getting mixed up with the requirement to have a visa which is valid for more than 6 months.
The General Requirements for granting of a Schengen Visa are:-
- The applicant must be resident in the UK.
Foreign nationals residing in the UK must have been granted visa leave to remain for more than 6 months.
- The applicant's UK visa must exceed the return date of the proposed trip by more than 3 months
- The applicant's passport must exceed the return date of the proposed trip by more than 3 months and must have a full blank VISA PAGE for the visa.
If the applicant is in the UK as the spouse of an EU national, they will be required to produce an original marriage certificate, together with the original passport of their EU spouse.
The 'standard issue' Schengen Visa is a 90 day visa with six month validity.
Depending on the application and also the individual Embassy, it's very often possible to secure a multiple entry visa with validity up to 5 years.
Each 'visit/trip' validity will always be a maximum of 90 days 'stay' in a six month period starting with first entry.
A Multiple Entry visa allows the holder to make multiple visits during the period of visa validity, provided each 'stay' within the Schengen zone does not exceed a maximum 90 days in any 6 month period. (unless specific visa restrictions apply).
This 90 'stay' can be divided into as many separate 'trips/visits' as wished by the visa holder. Means that leaving the Schengen-zone between 'trips/visits' and then re-entering via different points of entry.
However, if you use up your 90 days 'stay' allowance all in one go, you'd need to wait 3 months before being allowed to enter the Schengen zone again.