If you need your script to be a certain length just try reading it out loud with a watch before you send it. Be realistic about content and timing. If you can’t fit your copy into 30 seconds chances are I won’t be able to either! ;-)
Spell out odd words, names, places, web sites, etc phonetically so that I know how it is to be pronounced. For example do you want your web site addressed delivered as dot O-R-G or .org.