If the target sequence is 1,000 nucleotides long and there is only one copy of the template, it is going to take longer to generate the 1,000 tagged fragments.
Having more than one template to work from makes the Sanger protocol more efficient. If the target sequence is 1,000 nucleotides long and there is only one copy of the template, it is going to take longer to generate the 1,000 tagged fragments. However, if there are several copies of the template, in theory it will take less time to generate all 1,000 of the tagged fragments.