And DEFRA told me that it had to be done 30 days after the vaccination, which is done immediately before the microchip. Either way I think no matter who you talk to or what you read the true time period is 7 months. I just received my cats 3 weeks ago over to London so perhaps it has changed, or maybe it is different with dogs than with cats. But, having just gone through this, and speaking to both DEFRA and my vet, I was told it had to be done a month later. It is always better to err on the side of caution anyway.