Timing is paramount, particularly in the sphere of space exploration. Each mission can be likened to a complex puzzle, requiring each piece to slot perfectly into place for the broader picture to emerge. To ensure all parts align just right, there are two significant types of checkpoints used: ‘No Earlier Than’ (NET) and ‘No Later Than’ (NLT). These terms effectively bracket the ‘earliest’ and ‘latest’ dates for task completion. This article reviews these critical markers relative to their importance in maintaining the timely progression of space missions and ensuring the successful attainment of their objectives.