After how much time can a skilled sales executive get promoted: 1 year or more?

It depends on various other factors, such as motivation by the employer, access to the information, support, incentive plans etc.
If every thing is good and the sales executive likes his job then definitely he will get promoted in one year.

I think its not related to any duration of time but it depends on2 factors , FIRST what achievements he / she did which have added value to the company , SECOND what are the creativity he / she made which affects the cycle in his / her division and move the trend of it to top or to a higher point more than have been reached during the last year for the company , Finally by the above2 factors the revenue will be increased and some costs will decreased which by default affects the financial status of the company , that's will lead to be promoted not only from his / her manager but from the others top management according to what he / she did to the company since joined the company regardless when was that or the date have been hired to the company.

one year to assess his targets achieved or not

Depends on them and their calibre.

i think1 year is enough for that.