It's possible you may need to re-paste, but that depends. What did you use for thermal paste? For example, Arctic Silver 5 usually requires up to 200 hours for "cure" time. Others require no cure time. So, it depends on what paste you used. Check the website for the manufacturer of the paste. They should have the cure time for their products somewhere in their product info or support area.
This is the statement on Arctic Silver 5:
"Then the compound thickens slightly over the next 50 to 200 hours of use to its final consistency designed for long-term stability."