Firstly, thank you for pointing me to the delta documentation. The target module purpose is to calculate date/time differences

#1 how does the difference manifest itself

Original in 5.10.0 (I added the line that says "comparing..." 
1..60
ok 1 - use xxx::DateDelta;
# 
# comapring 4.000000 to 4.000000 at 0 func=seconds prec= type= field=s
+econds
ok 2 - seconds() (with time)
# comapring 4 to 4 at 1 func=seconds prec=trunc type= field=seconds
ok 3 - seconds(trunc) (with time)
# comapring 34298704.000000 to 34298704.000000 at 2 func=total_seconds
+ prec= type=total_ field=seconds
...
1..60
ok 1 - use AMG::DateDelta;
# 
# comapring 4.000000 to 4.000000 at 0 func=seconds prec= type= field=s
+econds
ok 2 - seconds() (with time)
# comapring 4 to 4 at 1 func=seconds prec=trunc type= field=seconds
ok 3 - seconds(trunc) (with time)
# comapring 34298704.000000 to 34298704.000000 at 2 func=total_seconds
+ prec= type=total_ field=seconds
ok 4 - total_seconds() (with time)
# comapring 34298704 to 34298704 at 3 func=total_seconds prec=trunc ty
+pe=total_ field=seconds
ok 5 - total_seconds(trunc) (with time)
# comapring 25.066667 to 25.066667 at 4 func=minutes prec= type= field
+=minutes
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But when I run on 538.2 I get

t/test.t .. 1/60 #
# comapring 4.000000 to 4.000000 at 0 func=seconds prec= type= field=s
+econds
# comapring 4 to 4 at 1 func=seconds prec=trunc type= field=seconds
...
# comapring 571645.066667 to 571645.066667 at 6 func=total_minutes pre
+c= type=total_ field=minutes
# comapring 571645.000000 to 571645 at 7 func=total_minutes prec=trunc
+ type=total_ field=minutes
# comapring 9527.417778 to 23.417778 at 8 func=hours prec= type= field
+=hours

#   Failed test 'hours() (with time)'
#   at t/test.t line 97.
# Expected 23 got 9527.417778
# comapring 9527 to 23 at 9 func=hours prec=trunc type= field=hours

#   Failed test 'hours(trunc) (with time)'
#   at t/test.t line 97.
# Expected 9527.417778 got 9527
# comapring 9527.417778 to 9527.417778 at 10 func=total_hours prec= ty
+pe=total_ field=hours
/\/\/\/
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creating the class:

use Class::MethodMaker
  new_with_init  => 'new',
  get_set        => [ qw (
              _delta_date
              _delta_time
             )],
  boolean        => [ qw (
              _use_time_flag
              )
            ]
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and the function for hours looks like:

sub hours {
    my $self = shift;
    my $name = (caller(0))[3];

    return $self->_format_time((defined($_[0]) && $_[0] eq 'trunc')
                   ? '%hv'
                   : '%hd')
}
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