So 2pm (1400) + 1400 off SCR start at 0400, RAP must end by 1800 ( 0400 + 1400 ).
Say you are assigned a FDP with 4 flights at 0500. The combined RAP and FDP must have a Scheduled End Time no later than the following:
Enter Table B at 0400, with 4 legs the max FDP is 1000, add 0400, that 's 1400 which is less than 1600, so the End Time is 1800.
Now The FDP itself must also be legal. 0500 Table B will return 1200. So 0500 + 1200 will be 1700.
Use the lesser of 1800 and 1700, The FDP must be schedule to end NLT 1700.
This is all in 117.21.
Extensions in 117.19
The extension will not begin until you have reached 1700, Normally you can be extended by 2 hrs, which would mean an drop dead time of 1900, but in this case you would you would still need to end by 1800.