Clearly this will be determined by your business and your audience and you may have read that Facebook posts get half their reach within 30 minutes of being sent so pre-planning is an important step.
Here’s a quick guide to get you thinking:

PostingTime

You could review your demographics, factors such as age range, gender breakdown and geographic location may influence your decision.  What might the day make-up of your audience be – night worker or stay at home Mom!
Check out Facebook Insights for further statistics.

Did you know that as high as 80% of 18-44 year olds check their mobile devices as soon as they wake up?  Meal times are a good bet and it’s reported that over 80% of mobile internet users check their device while watching TV.  Accessing social media sites increases at weekends but remember you will be competing with other news feeds, family, friends and those favourite brands.  You could try catching your audience’s attention whilst they are travelling to and from work.

One last thought, timing your post will only be beneficial to you if your audience engages with the content – Remember Content is King.