As far as I understand, burst post basically means posting quickly. A lot of forums are spammed especially by excessive posting. Since you post 15 - 30 minutes between 8 hours and 12 hours every day, you definitely post burst. You should keep a post gap of at least one hour per day and 12 to 13 posts in 12 hours per day will be enough for you. and if you post with this in mind, your posts will not be spam or brust posts.
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If we talk about that if someone posts too quickly than he might be spamming the forum with low quality posts, it looks reasonable. As this way we can try to indicate whom to check. But when we start talking about which time gaps to make between own posts it is no more discussion about post quality, it is a discussion about how to imitate post quality. Nonsense! If I have something to say I will never look at clock to count if enough time past, I will say it when I have something to say. And if there is nothing to be said at all it is better not to say anything and not just to imitate quality with gaps and quantity and... what else should be there?