If" someone does have high bp, do the readings usually stay high the whole day/evening or do they lower at times to "normal".

Fluctuate: BP normally fluctuates. High BP is defined as "basal" bp, that is, BP that remain elevated, on average, at complete rest in a calm comfortable setting. BP is dynamic (always changing) and high levels during exercise is healthy/physiologic. High levels at rest are not. Conversely, BP averages are used, so occ. Normal pressure at rest with a high average still needs to be controlled.