In the previous chapters, they stated that their time has "stopped". thus aging and death cannot take them since they are no longer bound to rules to reality and physics. Due to this phenomenon, they gain the ability to time travel to a certain point time. Think of a timeline where there's a restrictions of where, when and how to get there as well as what you cannot wander around. Both Will and Anne are affected by this time displacement that everything is out of order towards them
@TheHiddenToad there still some who are trained to be sharpshooter during those times but yeah I doubt he will hit directly in the head more like the body is more plausible.