The routine from 424 to 42D delays for a second while keeping the display alive by calling the KIM ROM routine to display the value of cells F9,FA,FB on the display. On my KIM, the value of 45 was found to be the best, 46 is too slow, 44 is too fast.
If you need to adjust yours, hold the [RS] key down for more than 1 second until the display flashes, this indicates that the write protection to the EEPROM is off. then enter [AD] 425 [DA] and type your new two digit delay value.
To have a more precise delay, a nested loop containing nops would need to be placed inside the existing loop. This would increase the byte count though.
The time display routine would look like this. To adjust the time, change the LDA $44 and LDA $90 lines. The first one is a coarse and the second a fine adjustment.
LDA #$44 STA *$28 L1 JSR $1F1F LDA #$90 STA *$27 L2 NOP DEC *$27 BNE L2 DEC *$28 BNE L1 JMP START