In the year 2017 there was amendment made in the act by the government and that will be implemented accordingly the CII.

Cost Inflation Index (CII) for FY 2018-19/ AY 2019-20 Notified by CBDT at 280 (Base Year 2001-02)

The criteria of 36 months have been reduced to 24 months for immovable properties such as land, building and house property from FY 2017-18.

So your previous tax will not applicable because you have done reinvestment. So again if you sell your property in current year it will be held as short term period and tax accordingly.

1. The previous LTCG on property transaction is already capitalized and the account is closed  & final and will not have any implications on the new sale in Dec-2019, wherein you would be entitled to again claim LTCG, only on one house transaction.

The property purchased as an investment to save capital gain should be held for 3years not 2 years. 

If you sell the property before 3 years holding , capital gain tax shall be charged on the sale of previous property. Exemption availed by you earlier shall be withdrawn in the year of selling the new property (within three years limitation).

Before budget 2017 capital gain on sale of immovable property was as follows. 

Held less than 3 years - short term Cap. Gain

Held more than 3 years - Long term Cap.  Gain

After budget 3 years period has been reduced to 2 years. 

This is relevant for determining the nature of capital gain whether short term or long term only. 

Now Note carefully here.  

No change has been made in exemption of capital gain provisions. 

Investment in new property - The new property should be held for 3 years from the date of purchase or construction. 

If you want to avail the exemption of capital gain you should hold the new invested property for 3 years. 

Hope this will clear your doubt. 

If capital gain is more than cost of new assets :

If you sale the new property within 3 years it's purchase or construction,  entire sale value shall be treated as capital gain, cost of the new assets in such case shall taken as Nil. 

If capital gain is equal or less than cost of new assets :

In case you sale the new assets with the said three years,  cost of the new assets shall be reduced by the amount of capital gain while determining the capital gain in respect of the new assets. 

If you want to avail the full benefit new assets must be hold for three years .

Taxpayers utilising this provision to avoid capital gains are required to not buy within one year any other residential house or a flat or should not construct within three years any residential house from the date of transfer of the original capital asset. Also, the lock-in period for the new residential house so acquired is three years. Hence, the newly acquired house should not be so sold or transferred within a period of three years. If transferred before three years, the entire capital gain would become taxable.

With effect from assessment year 2018-19, the period of holding in case of immovable property, being land or building or both, is reduced from 36 months to 24 months, to qualify as long-term capital asset. 

To claim exemption under section 54, the taxpayer should purchase a residential house within a period of one year before or two years after the date of transfer of old house or can construct a house within a period of three years from the date of transfer.

The LTCG can be claimed in a different assessment year also for selling the second property.

Yes you have completed the same

1. LTCG can be claimed once in Two years for only one Residential House.  This you can claim repeatedly (and not once in life time).

2. Presume you have Three houses, THEN you can claim LTCG only for 1st house AFTER the First Two years, of registration date of Sale Deed (not agreement to sale). Similarly you can claim LTCG for 2nd house AFTER the 2nd Four years and so on.

3. Though it is simple, STILL for understanding deeper technicalities, you would have to have a one-to-one talk with a local CA, specializing in Taxation matters.

Exemption will be reversed if you sell this new property within three years of purchase and capital gains from sale of the new property will be taxed as short-term capital gains.

AND LTCG can be claim once in lifetime.

If a property is sold within three years of buying (acquiring) it, any profit from the transaction is treated as a short-term capital gain in the hands of the individual.This is added to the total income of the owner and taxed according to the slab rate applicable to him.For those earning over Rs 10 lakh a year, this shaves off 30% of the profits from the sale consideration.

As per new amendment you have to hold the new property for duration of 2 years and you can sell the property now without worrying about capital gain tax.

1. Same shall be decided from.date of agreement so yes you have fulfilled the criteria of 2 years by investing into the property in financial year 2017-18 the same was changed to 24 months from 36 months.

You can freely sal property after completion of 2years holding it shall he considered as long term capital gain only