what time do deleting domain names drop each day?

There is no specific time each day that a domain is deleted.  There
are a lot of factors that dictate how soon a given person will no
longer be able to resolve a deleted domain name.

It usually goes something like this:

1. Customer submits a request to their registrar and/or hosting
company that their domain name be deleted.  A registrar is the company
that you actually purchase the domain from; this is often the same as
your hosting company. This is a list of registrars.
http://www.internic.com/regist.html

2.  The registrar submits the deletion request to the root servers
controlled by ICANN.  These entries are deleted and added continually
throughout each day.  If they are also hosting your site they will
delete the DNS records that they have on their servers.

This article will explain the "root servers" if you are not clear on what they do.
http://www.internic.net/faqs/authoritative-dns.html

3.  As soon as the DNS records are deleted from the root servers all
other DNS servers on the internet will start to drop that domain from
their registries when they update.  This last step of the process can
take days as the change is replicated throughout the world and caches
are cleared.

When any given person notices this change will depend on what DNS
servers and resolves they connect to and how often they are set to
update.  Normally 24 ? 72 hours.

If you are looking to get a domain that some else is dropping there is
often a 30 grace period where no one can register the domain.  This is
to ensure that the domain was not erroneously dropped.  It gives them
time to correct the mistake.
http://www.afilias.info/faqs/rgp

I hope that this has help to give you a fuller understanding of the
process and answers your question.  If you require any additional
information please post a request for clarification and I will be
happy to help.

Thanks!