Hi. Yes I am sure that this can be done but not exactly a feature of Dynamic Registration, actually a feature to schedule a page or module for a start/end date within DotNetNuke directly.
Here are the basics:
Add two text modules to a page and the registration module.
For text module one enter something like: Registration will begin on June 30th, please come back then.
for text module two enter something like: Registration has now ended, please contact support for more information
Setup the registration module as you wish.
Then. Under each modules 'Settings', 'Advanced' you can set a start and end date for the module. You could set the end date for text module one to be June 25th for example, then set the start date for the Dynamic Registration module to be June 25th and an end date of June 30th'. Finally set a start date for the 2nd text module to start on June 30th. This would show a before/after text message to the user when registration is not active, and the registration module when registration is active. I don't know how to do this with the standard DNN registration but I know you could with Dynamic Registration since its a seperate module.
-Chad