I have always been tempted to program my I-phone timer to play Mozart's death march, but maybe just get the lights to blink like intermission at an opera.😀
Most wisdom on this suggest a desk clock that you can see, but the patient can not. Have it in the line of sight toward the patient so you can look at it without turning in your chair. You don't want to let the patient become clock focused as they tend to either avoid material near the end, or worse, drop bombs in the last minute.
We all hate saying "I see we are about out of time, but we can continue with this next session..... but this is bound to happen regularly.