The USDA puts a handling/holding time on foods, 4 hours, that is generally safe over a broad range of conditions. But that depends a lot on the food and preparation conditions. Spam or any cooked protein, handled in a sanitary fashion, clean hands, board, knives, wrapped well and so on can go longer than four hours with little risk. How many people have gone to a Super Bowl party and the Six Foot Sub Sandwich sat on the table 8 to 10 hours and nobody ends up sick. Now, a don't give a damn, dirty food service worker assembling on a cross contaminated work station and that Spam or Sub could make you very sick after 1 hour at room temps!
Spam for MUSUBI, Hawaiian Spam Sushi, is cooked, usually grilled and sauced with a Teriyaki Glaze and caramelized. It is then rolled in Rice. The Spam is not usually the issue, cooked to sterilize, lower in available moisture and salty, but the Rice is. Rice can easily be infected with Bacillus Cereus Spores. These survive cooking temps and can activate if left at room temp for more than 4 hours.
Your choice to cool smoke a cured and cooked, salty, meat like Spam for just three hours represents little risk to a healthy individual. Use good judgement though, Hot Smoke, 180°F+ if young Children or Elderly folks are going to eat it...JJ