Since your triathlon training plan is the focus of your efforts, keep your time at the gym tight and efficient. Two 45-minute sessions each week is all you really need at this point.
When it comes to maintaining strength, target compound exercises—deadlifts, squats and shoulder presses. Exercises that use the big muscle groups are your friends. Remember, your races take priority, so there is no need to set a personal weightlifting record during this time.