SSL certificates

I wish to use client side PKI certificates. I would like to generate
said certificates myself since I know the people that will be
authenticating. My question is that when a certificate is generated by
myself and installed on the client machine does that machine make a
check on the validity of that certificate only once (when it's imported)
or every time that the certificate is used (every time the site is
accessed? The reason I ask is I want to know whether I will need the
generating server to be online 24/7.

Any good online FAQ? I found a few very bried ones lacking in technical
information such as handshakes etc. I dont mind finding out for myself
if someone can point me in the general direction.

Thanks.

 

(snip)

read all about openssl so dont worry I know everything I need and a test
environment is in the process of being sorted out!

the docs for openssl pretty much cover the stuff I couldn't find
elsewhere on the web when dealing with TSL, SSL v2 and SSL v3 to a level
necessary to understand what's really happening rather than just an
empirical overview.

Cheers anyway (plus if anyone's got any info to add, don't worry about
following up!)