Dogs gestation period is 63-69 days from the tie. The mom's temperature may drop to 99 degrees 12 to 24 hours before delivery. She will also show nesting signs, such as ripping up paper, blankets etc. and she will become restless. Once active labor begins she should have a pup within two hours, any longer than that and there is a problem. Boxers tend to have problems birthing because of the square heads so you ought to be aware of that. Getting an x ray of how many pups she is carrying will be a big help to you so I would consider this.
I am going to direct you to a site that talks of pregnancy, what to have ready for birthing, delivery, and how the pups grow from week to week to better assist you.