This is quality!
Temporal Tower: love the Mixolydian here along with the 8-bit, it gives a sort of GB Pokemon vibe. A good title theme!
Present Plains: Using the motif from Temporal Tower, but more energetic. Strong overworld vibes.
Chrono Fiend: This is one hell of a cool battle theme. Loved the reverse piano sounding sfx.
Time is Money: knew this was a shop theme before even reading the description! Very groovy.
Where Time Can't Reach: this is one cool rhythm. Love when the pads come in for that full sound.
Reminisce: Very dreamy. The minor plagal cadence like you said adds a nostalgic feel.
New Dark Ages: Very cool final boss theme. Those reverse samples are a great touch. The meter here is dope. bVI-i section (after 3:26) really gives me that classic NES/GB final stage feel. Bells help add more of the time connection.
Great work!