Bad when a pet scan takes a long time? My grandfather's pet scan was only scheduled to take 1 hour, but instead it took 4 hours. Is that a bad sign? It was the second pet scan he had after the first showed a malignant tumor.

Not a bad sign. Generally, if a pet/ct scan takes longer than 1 hour, it is for technical or patient motion reasons. The camera might have had a problem, or the patient may have moved and part of the scan repeated, or more of the body (legs) imaged. Of course, after the initial injection of f-18 fdg, the patient should wait 1 hour for the drug to accumulate in the tissues and clear from the bloodstream.
No necessarily. It does not have any clinical significance. It could just be related to setting things up or preparation before the pet begins. The important information is the findings. I would not focus on the amount of time the procedure took.
While . While the pet scan itself generally takes about an hour, the entire procedure always takes longer, since the patient usually rests quietly for about an hour after the radiotracer is injected but before the scanning begins. There are many possible explanations for the extended time of your grandfather's scan, and it is not necessarily a bad sign that the scan took 4 hours instead of 1 hour. One possibility is that activity was seen in parts of the body that might have been attributed to muscular activity, speech, or digestion, but the doctors wanted to be certain and so a delayed scan was performed. Another reason for a delay could have been to correct an underlying laboratory abnormality such as an elevated blood glucose level, which would interfere with the results.