The county auditor shall receive the returns and make the assessments provided for in this chapter within the time prescribed by law and for this purpose his office must be kept open to receive the returns of taxpayers from January first to April thirtieth of each year, except as otherwise provided, and the returns must be received throughout the period without penalty. He shall, for the purpose of assessing taxes, attend at a convenient point in each township or tax district as many days as may be necessary and for the remainder of the time allowed by law he must be and receive returns at the county seat. He or his assistant may give thirty days’ public notice of the days upon which he will be at the several places designated.