Burn time depends on the length, thickness, composition, and construction of the incense stick. Two sticks that look similar can burn at noticeably different rates, so the maker's stated burn time is the best reference when one is provided.
Room airflow matters too. A draft can affect how incense burns and where the smoke travels. Rather than choosing incense only by burn time, consider whether you enjoy the fragrance and intensity for the space. Whatever the duration, keep burning incense attended and positioned securely in a proper holder until it is fully extinguished.
Burn time and scent duration are not the same thing. The stick can finish smoldering while some fragrance remains in the room. Conversely, you may find the room comfortably scented before the whole stick has burned.
For a shorter session, follow the maker's instructions for extinguishing the incense early instead of leaving it unattended to finish. A smaller stick or a product with a shorter stated burn time may fit your routine better. Choose based on the amount of time you can stay with it as well as the scent you like, and allow the holder and ash to cool afterward.