Suspended means the match had started and was then delayed (bad light, rain) and will be continued from where it was left off. Postponed means it hasn't started and will be played later, usually the next day.
As far as grading I don't think it makes a difference at any book. Most books have a requirement that a match must go within 72 hours of the scheduled start, but you should always check just to be sure.
It is different from baseball, since the players play only one match and not a series there is no confusion in letting the bet stand up to 3 days.