I’m going to try and use somewhat of a scientific approach to this

From the original film to LBT II, one could assume little to no time has passed. We can base the time spent between the original film and the first sequel on the time that it takes for a dinosaur egg to hatch. I found this source
Dino Eggs Hatching that states that a dinosaur egg could’ve taken 45 to 80 days to hatch, depending on the species, let’s round it up in the middle, and give them about 60 days (two months), between The Great Valley Adventure and The land Before Time.
The events in The Time of the Great Giving, could’ve taken part right after LBT II, and may have taken about a month to take place, from the time the sky rocks fell to the fire. From LBT III to Journey Through the Mists, we need some time for the trees to regrow. In the real world this would take years, if not decades, but, for the sake of the plot, let’s say a year has passed. So, we’re up to 15 months. LBT V, could also have happened straight after LBT IV. If we give a two month interval for the events of LBT IV to take place, and for Ali’s herd to leave, that takes us up to 17 months, plus an additional 6 months for the leaves to grow and for the actions of The Mysterious Island to take place.
It’s LBT VI’s turn and 23 months have passed. The actions in VI and VII are very contained and don’t show many great disasters, we can give two months for each of them, taking us to 27 months and lending us in the heart of Winter. The Big Freeze needs about three months for the snow to melt, so an additional five is added, making it 32 months (2 years and 8 months) by the time Journey to the Big Water comes around.
The next sequels can also be sequential since they don’t have any major time jump. So, giving two months per sequel takes us to 3 years, before LBT XI. Because the tree sweets tree grows back its flowers, one can argue at least a year has passed, taking us about 4 years between the original film and The Wisdom of Friends.
To recap:
LBT – LBT II: 2 months
LBT II – LBT III – 1 month
LBT III – LBT IV – 12 months
LBT IV – LBT V – 2 months
LBT V – LBT VI – 6 months
LBT VI – LBT VII – 2 months
LBT VII – LBT VIII – 2 months
LBT VII – LBT IX – 5 months
LBT IX – LBT X – 2 months
LBT X – LBT XI – 2 months
LBT XI – LBT XII – 12 months
LBT XII – LBT XIII – 2 months
LBT XIII - LBT XIV - ?
Total: 4 years and 2 months
What do you guys think?