The warlock monster can inflict the closest investigator with Cursed during the Reckoning Phase. Since conditions are handled after monsters during the reckoning phase, can I then roll to see if I can get rid of the Cursed condition during that Mythos phase, or do I have to wait until the next Mythos phase?
Page 10 of the Rulebook:
Resolve these effects in the following order: Monsters, Ancient One sheet, Ongoing Mythos cards, and lastly investigator possessions and Conditions.
Would suggest that you can, however, in the Reference Guide it states:
If a Monster is spawned or an investigator gains a component while investigators are resolving reckoning effects, they do not resolve the reckoning effect on that Monster or component.
Since cards are components, you cannot get rid of it on this turn.