Sometimes at the saunas, I usually go late at night and try to time it so that I can be the last customer of the girl's shift. If I am lucky, she may have only done 1-2 customers before me hence would not be so tired. But if she is tired, she can always compensate her tiredness by walking on my back.
By being her last customer of her shift, we can both enjoy the HE part in a leisurely and relaxed manner. Plus because it is late at night, she may accept my invitation and sleep/rest with me for awhile (anywhere from 15mins to until the next morning) and not worry about having to get up to service another customer.