It's established very early on in the show that there has not been a proper spring or fall in a very long time. Only blazing hot summers and freezing cold winters.
The lyric change comes at the tail end of Act 2, during Wait For Me (Reprise), when Hades and Persephone discuss "trying again"/fixing their marriage. For as far back in the show's development as I can remember, Hades has always had the line "It's almost spring. We'll try again next fall." Tonight, the line was changed to "It's time for spring. We'll try again next fall."
I'm not sure how to put into words why I think this is such an effective change, but I can try. I feel like it better communicates that Hades now understands why she has to go, and that he cannot hold her below for an obscenely long period anymore. It's not that spring is approaching and she needs to leave; it's that it's time to finally have a spring, and he knows this now. He's reminded of what spring was like when he first fell in love with Persephone. He sees now that it's time for the overworld to have that again.
If that makes any sense.
Normally I'd say I'm reading way too into things, but it's such a tiny thing that they've decided to alter after the lyric being unchanged for years. So I'm chalking it up to their incredible attention to detail. It made me tear up, so whatever they were going for definitely worked.