NHL Insider Elliotte Friedman was very quick to point out a few moments after the original announcement that this roster move is very much tied to the salary cap and that Marner is eligible to be activated from LTIR tomorrow with the intention of having him return to the lineup at some point this coming week.
This falls in line with a report directly from Maple Leafs head coach Sheldon Keefe this week, confirming that the plan for Marner is to get him into the team's next practice, which is scheduled to occur on Tuesday, before re-integrating him into the lineup. Keefe stated that he wants Marner to get back up to speed in competitive situations prior to re-joining the team, meaning that he'll likely miss Monday's game against Florida.