It's the difference between optimizing for latency and optimizing for throughput. Clients tend to want to optimize for latency rather than throughput. To them, a "good enough" analysis by tomorrow morning (before some important meeting) is often much more valuable than a perfect analysis tomorrow afternoon (after the meeting is over).
This is true, but it sounds as though this is just because your clients are facilitating this kind of behavior in their clients by not scheduling the meeting for a time when the material can be prepared without people working in their family time.
Presumably they do this because they expect to be able to lean on you when the work needs to be done.
