I think I may have figured it out. I made the following changes: 
class_type 'DateTime';


subtype 'DT' => as 'Maybe[DateTime]';
coerce 'DT',
    from 'Str',
    via { DateTime::Format::DateParse->parse_datetime($_) };

coerce 'DT',
    from 'Int',
    via { DateTime->from_epoch( epoch => $_ ) };

... 

has created_time => (
    is       => 'rw',
    isa      => 'DT',
    required => 0,
    coerce   => 1,
);

# and then in the subroutine I posted earlier:

...

for my $post_id ( keys %$post_response ) { # changed to unblessed 

...

[download]
But I'm now getting an error about something else in the module. So I will follow up as necessary :)

In reply to Re^3: Attribute does not pass Type Constraint by PerlSufi
in thread Attribute does not pass Type Constraint by PerlSufi

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