Factors to consider when determining a full tree removal:
Most factors with how they affect amount of time required to complete a tree removal. More dangerous jobs require more planning and more time to complete the tree removal. More dangerous jobs require more effort and time to complete correctly. If trees are in a bad location this will require much more time to remove and trees that are near homes or other structures will involve rigging and larger equipment and procedures like lowering sections of the tree with ropes this will also require more time to remove the trees. Often there is no other option to safely remove a tree other than bringing in large equipment such as a crane and also may add cost to the project.
The larger the tree the more time it will take to remove it and this generally adds more cost as well.
The location of the tree is also a factor;
The debris, branches and leaves, that fall off the tree are usually fed into a wood chipper which pushes the chips into the back of a truck. The truck and chipper cannot always be positioned close to the tree so when the tree is in a backyard or next to a home the farther the tree to be removed from the truck in the chipping machine the longer it will take to drag the debris also increasing the time and possible cost of the job.