My cholesterol was higher than 'they' would like a few years ago but I refused to take medication - everything I do is healthy on the whole and I am not over-weight. As for BP, they rarely check mine and it is usually OK. Certainly DH and the instructions suggest that BP should be taken at the same time. Obviously if someone is more energetic and needs to check whether the readings varying because it's stress related is different, but once that has been sorted, the same time of day and not immediately after food is recommended.
The body uses up different energies after eating which could skew the BP readings!