That’s just hearsay. Do you have proof that it’s actually true?
Thats either was true at a certan time and changed or its simply an old myth.
Relic and data sited despawn (and presumably respawn) in rage of 0.5-2 hours after the first can is destroyed or opened, regardless of DT.
Easy to test if you have doubts.
What is it that led you to belive that sites spawn with their rewards already set?