Best of times

What do these ones mean? I'm confused with 'best of times' especially when 'times' is plural.

1. A perfect placement is difficult at the best of times.

2. Perfect placements is difficult at the best of times.

"At the best of times" usually means something like "in the best circumstances or situation possible."

I think the first sentence means that finding the perfect job placement (placing someone in the ideal job for him or her) is difficult under even the most favorable circumstances. (The type of placement might be personal or academic rather than professional, but professional, i.e., having to do with a job, was what I thought of first.)

The second sentence is not grammatically correct. "Perfect placements are difficult at the best of times" would work. Placements are plural.

They carry the same meaning without a context.  Number 1 is a bit more 'pointed', i.e., would tend to be said for a specific incident.  Number 2 might be said in a given incident, too,  if the point of saying it was to characterize the incident as a general type of incident.