According to OSHA, the exposure time limits are [3]: (these are A-weighted, most home theater measurements are made with C weighting, which typically gives higer readings for broad spectrum measurements).
Exposure Time Exposure Level (measured in dB SPL)
8 Hours------------------90 dB SPL
6 Hours------------------92 dB SPL
4 Hours------------------95 dB SPL
3 Hours------------------97 dB SPL
2 Hours------------------100 dB SPL
1.5 Hours----------------102 dB SPL
1 Hours------------------105 dB SPL
.5 Hours-----------------110 dB SPL
<.25 Hours---------------115 dB SPL
[3] United States Occupational Safety and Health Administration. Occupational noise exposure, Standard Number 1926.52.
Link to standard.