To move from commitment to action, planners must think about the future and decide when to initiate. We demonstrate that planners prefer to initiate on upcoming days that immediately follow a temporal boundary. For example, aspiring dieters who considered a time horizon from Thursday, February 27th to Tuesday, March 4th showed expectation increases from Days 4 to 5 (Sunday to Monday) when induced to think of weekdays and from Days 2 to 3 (February 28th to March 1st) when induced to think of calendar dates. Using both causal steps- and moderation-based approaches, we demonstrate that this occurs (in part) because planners neglect situational constraints when evaluating initiation opportunities after (vs. before) temporal boundaries. A field experiment demonstrated a costly consequence: Aspiring dieters were more likely to sacrifice 1 week of access to an expensive weight-loss program if it allowed them to start on a day they perceived to follow a temporal boundary.