Well, loading POSIX which is an XS/C module is afaik pretty light. You could always put something like

END {
use Data::Dumper;
print Dumper(\%INC);
}
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in one of your modules and have a look at what is loaded. Id guess you'd be surprised. :-)

Is it not using posix only for this that would make the code as a whole bloated ? .

How does

use POSIX qw(strftime);

print strftime "%Y-%m-%d",localtime(time);
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Make your code bloated? Id bet the optrees and the rest created by your code to do the same thing are actually a lot bigger footprint than the precompiled from C POSIX library. Also, of the two which would you prefer to maintain?

Now look, if you are writing scripts for a high usage web set, or something that has to have really fast load times then fine we can quibble about loading POSIX or something like it. But for the rest of the time I dont really see much room for even thinking about how long modules load, almost any task that is hard to do will take so much longer than the load time that its not worth caring.