Please change splunk_app_addon-builder/bin/ta_generator/input_meta_util.py lines 822-823 (regex and message for validation of the default interval field) to allow cron expressions on top of integers.
The wizard needs changes too to let the default value be a cron expression as well, for some reason it's two entirely separate sets of validators that I didn't dig into, I'm sure you'll locate the code.
