When planning your Snapchat posting strategy, you should consider the type of content you are posting, e.g., if there's anything lewd, it shouldn't be posted in work hours, as people will be less likely to check it. If it requires people listening to the Snaps, then they should be posted at a time when people will be able to listen to the content (also likely outside of work hours). Also consider your follower base--if they are 18-30 in general, you will want to either post at lunchtime (when they check their phone) or between 4 and 7 pm (between finishing work and eating dinner).
In terms of length of story...
There isn’t one defining rule for how many Snaps make up a story--the most important consideration is how interesting your content is. For example, 10 Snaps showing 10 aspects of an awesome music festival might seem short, whereas 10 almost identical, dialogue-heavy frames of someone’s breakfast can seem like a marathon effort to watch.
Alongside having interesting content, a story needs to make sense for a viewer and have a beginning/middle/end. Stories without context or a lack of direction tend to have FAR LOWER completion rates.
One thing that some of our clients have found success with is spacing out their Snaps throughout the day (only if it doesn't affect the story if Snaps are spaced out). This ensures that their stories are constantly bumped to the top of people's feeds (as the Snapchat stories feed on your phone is top down in chronological order).