Provided that, if within the time specified any such duly authorised agent deposits with the Collector the necessary expenses of making copies of the said maps or papers, the Collector shall order such copies to be prepared, and as soon as they are prepared shall cause a notice to that effect to be posted at his office, and the said agent shall be allowed such time as may be specified in such notice, not being less than fifteen days from the posting thereof, for the purpose of signing or of giving in a written statement of objections.