When was Hamlet set?

Your question was pretty confusing, since you ask what
seems to be a relatively straightforward question about time period in which
Hamlet was set, yet you follow this with a mention of
post-structuralism in your clarification and tags.  I fail to see the connection between
time period in which Shakespeare might have set Hamlet and
post-structural analysis of the play, since post-structuralism was a 20th century
movement in literary criticism.  Please re-frame your question about post-structuralism
as it relates to Hamlet and then post it for
answer.

Meanwhile, here is my response to your question,
"When was Hamlet set?"

Shakespeare
makes it clear that this play is set in Denmark, but he does not specify time period. 
By examining the available source material that scholars imagine Shakespeare might have
used to create the plot of Hamlet -- and a significant potential
source, the Ur-Hamlet, is lost -- you might be able to create a
guess about what time period these characters might originally have been created to
exist in.

However, Shakespeare was never concerned with
time period in staging his plays.  All of his plays (including the ones "set" in ancient
times like Julius Caesar, Antony and
Cleopatra, A Midsummer Night's Dream, King
Lear and Pericles, to name a few) were costumed and
presented as if they were taking place right in the "modern" Elizabethan world in which
Shakespeare lived and worked.  His characters also spoke in the ways that people in
Shakespeare's society spoke, no matter the place or time or culture they were meant to
exist in.

So, no matter what you might unearth about the
actual "Prince of Denmark" and when he might have lived, you can be sure that, for
Shakespeare, the time was "now," and the dress and conversation was 100%
"contemporary."

For more on the historical background of
the source material Shakespeare may have used to create Hamlet and
the use of "modern" costuming at Shakespeare's Globe, please follow the links
below.