The first limit is that you have 45 days from the date you sell the relinquished property to identify potential replacement properties.  The identification must be in writing, signed by you and delivered to a person involved in the exchange like the seller of the replacement property or the qualified intermediary.  However, notice to your attorney, real estate agent, accountant or similar persons acting as your agent is not sufficient.

Be careful in your selection of a qualified intermediary as there have been recent incidents of intermediaries declaring bankruptcy or otherwise being unable to meet their contractual obligations to the taxpayer.  These situations have resulted in taxpayers not meeting the strict timelines set for a deferred or reverse exchange, thereby disqualifying the transaction from Section 1031 deferral of gain.  The gain may be taxable in the current year while any losses the taxpayer suffered would be considered under separate code sections.

https://www.irs.gov/newsroom/like-kind-exchanges-under-irc-code-section-1031