Congratulations on the new job - hope it is going well.
The time you need to be in your new job before moving depends on many factors such as the type on employment (is it the same field as your previous job, have you moved job to improve your earnings etc...), if there is probation period, how much you need to borrow in relation to your income and how much deposit you are able to provide.
Usually, a new Lender would want a probationary period to be over, but in many circumstances this requirement could be waived if it can be shown that the job move was a career enhancement in the same field and all other aspects of the application are good.
As ever, give us a ring on 0845 345 5705 if you want to discuss your exact circumstances.
Louise