Originally posted by i83N But I have SDHC and stil getting 5-8minutes(depends on outside temperature)
It doesn't matter if you have SD or SDHC. They both use FAT32 (or even FAT16), which is a 32-bit file system, and thus cannot use memory addresses of more than 32 bits (4GB). Only SDXC uses 64-bit exFAT to allow larger memory addresses.
The sensor or battery cannot possibly accurately estimate the time to overheat/battery failure. They are not that precise, nor designed to detect highly variable ambient conditions, nor can they predict what you will be shooting (different scenes produce very different stresses on the sensor). If it shutdown to prevent overheating, it would either happen when it actually overheats (which is unpredictable), or be hard-coded to do so (like Sony and others do), in which case the time would be invariant.