This is directly from the CAA Medical Department's web site :
Refractive Surgery
The CAA does not recommend refractive surgery to gain a medical certificate to fly. The decision to have this type of treatment must be between you and your eye specialist. In fact the certification limits of eye correction with glasses and the limits of refraction before surgery are the same, so it is not possible to gain a medical certificate by having refractive surgery, that you would not have obtained by wearing glasses. However, if you have had refractive surgery, Class 1 certification will be considered three months after a LASIK procedure, (provided an assessment including refraction has been carried out at two months post-operatively). Certification can be considered six months after LASEK/PRK for myopia (provided an assessment is carried out at three months post-operatively at Gatwick). is usually possible one year after other types of operation.
Please note that:
• the pre-operative refraction should not have been more than + 5.00 to -6 dioptres (applicants just outside this range should contact the CAA Medical Department for advice.)
• an assessment by an eye specialist at Gatwick will be required
This mentions the time-scales you wondered about. There is never any harm in contacting the CAA to ask about individual cases.