The Lightspeed and Time Force Rangers swapping jackets at the end of "Time For Lightspeed."
Carter: You got the jackets, now try the dance! [referring to the morphing gesture]
Time Force Rangers: Lightspeed! Rescue!
The first part of the finale when Nadira, with Trip's encouragement, helps deliver a baby causing her to question her father's hatred of humans and being the catalysis of her Heel–Face Turn.
Hell, the entire ending of the finale qualifies.
Wes's father coming around and admitting that he doesn't want Wes to follow in his footsteps and find his own path.
To emphasize this, in the first few episodes, money's all Mr. Collins cares about, to the point where Wes had to effectively con him into donating to charity and the Silver Guardians are only protection for those who pay, even at one point trying to buy the other Rangers into joining. By the finale, he is evacuating people into his limo and says the Silver Guardians are no longer a for-profit security force.
In "Nadira's Dream Date", otherwise a silly filler episode, we learn that, for all his racism, bloodthirst and general desire to see humanity crushed, Ransik is willing to put aside a bit of that hatred for Nadira's sake. If dating a power ranger is genuinely what his daughter wants, then that's what his daughter gets!
The Time Force cast was reportedly one of the friendliest in the show's history. Everyone got along famously, with the actors even saying there'd been talk of having them continue for an additional season.