#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=seconds
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=seconds
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 type=total_ field=seconds
ok 5 - total_seconds(trunc) (with time)
# comapring 25.066667 to 25.066667 at 4 func=minutes prec= type= field=minutes