I know how to set up a cron which calls a script every 2 minutes. For example:
*/2 * * * *
*/2 9.30-9.45 * * *
In your particular case you can use:
30-45/2 9 * * * [command]
For more complex setups I think it's generally better to move the logic into a script that Cron would call every N minutes and that would check the time and exit immediately if the current time is not within the defined range.