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If you are getting bored after a half an hour, ya ain’t even close to fully sustained attention on the breath. When our attention is fully sustained, there is no room for boredom. It’s akin to how engaged your mind is in an engrossing movie or during sex. And just like either activity, you get pulled into fully sustained attention. You don’t provide full sustained attention.
You aren’t going to reach jhana sitting like that. First of all, it requires many years of practice. Secondly, true jhana is only ever reached in a retreat setting and after multiple days of 10+ hours of sitting. Finally, even outside of a retreat setting, your practice times really need to exceed an hour or more (90-120 minutes is ideal) of unbroken sitting in order to effectively train samatha meditation. You can’t expect to run a marathon by practicing sprints.
This may sound like a lot, and it is. But nothing good comes without effort. People learn to play a pretty mean piano without ever needing to lock themselves away in a monastery. You can likewise develop a deep meditation practice in lay life. But expect it to challenging. There is only the hard way.