LTA exemption is available for only two journeys performed in a block of four calendar years. The block applicable for the current period is the calendar year 2018-21. So, from 2018 to 2021 you can claim, any two journeys for LTA Exemption. if you already claimed Exemption for 1 journey in 2018-19, than you can claim for second journey in 2019, 2020 or 2021 subject to fulfillment of other conditions and restriction as per sec.10(5).