Much of this "should" have been spelled out in the intital contract. Most of the time it is not.
How much money have you paid him/her? Did he/she tell you that they would not be there on such and such day? Like Jay said, are they awaiting goods or material? Did they communicate with you as to why they would not be there on such and such day?
I know what you might be thinking, to controll all variables a contract might have to be 15 typed pages long. Most don't get into many details, but mine always give a ball park time for completion.
As Jay so elequoently stated, you do need to give him/her the benefit of the doubt and maybe he she is sick, death in family or some other emergency. I hate to say this because I am a contractor too, but many many contractors do not communicate with the homeowner well and vice versa. This is not professional and creates alot of mistrust for each other.
If you are happy with the work so far, then I would be patient and wait alittle longer. Try to contact him/her and document all that you have done so far.
Consider this, when he/she shows up for work and if you get "testy" or he/she takes it that way, the job might suffer. So, if he/she does come back, handle the case very carefully. He/she might take the talking out of context and do a shoddy job. I would not pay him/her any more money until the job is completed or as the contract states.
I do appologize. In my business, my priorities are to communincate with homeowner extensively and be prompt and dependable and have a neat clean work site. I cannot tell you how important I have found this to be. Its even more important that the quality of job you are doing.