Spouse/partner (of a UK national or settled person) visas are issued for 2 ½ years. For this reason the timing of applying to extend is critical for those intending to eventually apply for ILR.
If a spouse/partner visa extension application is submitted too early, the new 2 ½ year visa may not stretch to the 5 year point. A further extension would then be required before applying for ILR.
To reach 5 years for ILR, an extension application should be submitted close to, but before, the expiry date of the first visa.
There is no specified limit on absences from the UK for spouse/partner visa holders applying for ILR. Instead, Home Office guidance states that limited periods of time spent outside the UK must be for reasons which are consistent with the intention to live together permanently in the UK. This could include time spent overseas in connection with the applicant’s or their partner’s employment, holidays, training, or study.
Home Office guidance for spouse/partner visa holders applying for ILR is specific to their circumstances listed in answer to initial questions asked on the 'Find out if you can apply to settle in the UK' page.