>You can increase timeout in the config manager (in the connection string), but it may be also better to try to fine tune this update statement.

The update statement is as its simplest. It update only one record based on the primary key. I believe SQL Server falls in sleep mode or release its cache when the traffic is almost at zero (in the middle of the night) and the next hit on the big table will take longer. I believe this is what was responsible for the situation.