Umamaheswara Swamy Vratham at Srisailam generally takes around 1 hour to 1 hour 30 minutes.
Devotees must reach the seva queue line at least 15 minutes before their booked slot time. The seva may not start exactly at the scheduled time, as it may take some time for other devotees participating in the seva to arrive.
If you are planning to attend Umamaheswara Swamy Vratham, keep around 1 to 1.5 hours for the seva, along with some additional time for waiting.