There should be an option (checkbox) to make a block act just like tnt. You should be able to change how powerful the tnt is, as well as how long it takes for the tnt to explode (only if possible).
MCreator issue tracker has been migrated to GitHub.
Existing tickets have been migrated to GitHub. Please open new tickets on the GitHub tracker instead. If you do not have a GitHub account, all feature requests and bug reports from forums are still considered and checked by the maintainers.