Players on the prospect roster can be promoted and demoted as many times as the GM wishes (unlimited call-ups and demotions), provided the player still meets the eligibility requirements for a prospect.
If the player is promoted once he has reached the age of 25 and/or has played in 25 or more NHL games, he must remain either on the active roster or in the reserves (if necessary a player must be dropped from the active or reserve roster to make space for the promoted prospect).
A prospect who has reached the age of 25 and/or 25+ NHL games may remain on the prospect roster during the season for as long as the GM wishes. At the beginning of the next season, any player on the prospect roster who no longer meets the eligibility requirements must be promoted to the active roster or to the reserve roster.
If the promotion of a prospect results in a team roster becoming illegal, the necessary move(s) to make the team legal (dropping a player, etc.) must be immediately made upon call-up.
For the 2012-13 season ONLY, a prospect who would have met eligibility requirements had there been no lockout (and the season had begun on time) is permitted to remain on the prospect roster until promoted or until the beginning of the 2013-14 season.