5. Night, Sunday, and Holiday Work:[78] No night, Sunday, nor holiday work requiring the presence of an engineer or inspector will be permitted except in case of emergency, and then only to such an extent as is absolutely necessary and with the written permission of the Engineer; provided that this clause shall not operate in the case of a gang organized for regular and continuous night, Sunday, or holiday work. 6. Absence of Engineer or Inspector. Any work done without lines, levels, and instructions having been given by the Engineer or without the supervision of an assistant or inspector, will not be estimated or paid for except when such work is authorized by the Engineer in writing. Work so done may be ordered removed and replaced at the Contractor’s sole cost and expense. 7. Absence of Contractor. During the absence of the Contractor he shall at all times have a duly authorized representative on the work. The Contractor shall give written notice to the Commission of the name and address of said representative and shall state where and how such representative can be reached, at any and all hours, whether by day or night. Whenever the Contractor or his representative is not present at any place on the work where it may be necessary to give orders or directions, such orders or directions will be given by the Engineer and they shall be received and promptly obeyed by the superintendent or foreman who may have immediate charge of the particular work in relation to which the order may be given. 8. Commencing Work. The Contractor agrees to begin the work covered by this contract within —— days of the execution of the contract and to prosecute the same with all due diligence and to entirely complete the work within —— days. It is understood and agreed that time is of the essence of this contract, and that a failure on the part of the Contractor to complete the work herein specified within the time specified will result in great loss and damage to said Sanitary District and that on account of the peculiar nature of such loss it is difficult, if not impossible, to accurately ascertain and definitely determine the amount thereof. 9. Liquidated Damages. It is therefore covenanted and agreed that in case the said Contractor shall fail or neglect to complete the work herein specified on or before the date hereinbefore fixed for completion, the said Contractor shall and will pay the said Sanitary District the sum of —— Dollars for each and every day the Contractor shall be in default in the time of completion of this contract.