The deadline for sending the notice depends on the type of lease.

The lender let the closing deadline lapse and we used the line of credit to purchase the property.

Right now, the properties in the list is cumulatively worth $2.4M and we're half way to our March 2016 deadline.

I met the deadline per the contract's demands.If they met my contingencies, the contract was binding.

Its a SFR with a motivated seller against a nearing deadline to sell.  

It took some time for the contractor to get everything itemized and get everything back in a timely manner, at this point I AGAIN passed my deadline to close so I had to request another extension which cost me $375 for a 2 week extension.

Good agents will also look for homes that aren't for sale and still fit your criteria, but that rarely results in a sale. 90% or more of all homes are bought and sold off the MLS with two brokers involved.An agents job is to educate you about the current market so you know what to expect whether buying or selling.An agents job is to help you make a good decision once you find a possible purchase by providing knowledge and insight you wouldn't otherwise know or even where to find it.An agents job is to make sure you understand the contracts you sign so that you don't get stuck in a bad deal or lose your earnest money because you missed a deadline.

Hitting the June 1 deadline shouldn't be difficult - the issue will be in assigning the purchase contract to the new entity.  

Also my plan was to pay it off well under the 15 year deadline and collect rent on it for the rest of my life.

If you sold a property held in an entity, then it would be Form 8825 and the accompanying depreciation schedule.It may be a good idea for you to file an extension (if you owe taxes, then make an extension payment) and then get with a CPA after the 4/18 deadline who can assist you with the filing of your tax return.