HM79
I always do my best at figuring things out on my own with the available tools, and being prepared for a last minute runway change, in most cases you will find in this type of airlines a fair amount of training going on, although the dispatcher does his best at calculating the RTOW, the pilots are often confronted with this question when they reach the airplane, we calculate it on a TO performance software, and if can get help with the runway prediction for departure time, we have a better idea of max take off weight.
most of the time spent preparing the departure is based on that runway,
preparing the FMS for normal and emergency situation, briefing for both conditions, preparing takeoff performance, and offloading cargo if there is an unexpected runway change. all those things can be done very quickly with experienced and efficient crews, but again consider there are plenty off pilots under training, some of them will never overcome that phase.