It should take about 2 hours to do the regularly scheduled RTRs; FRTR, shattering, tetragramatron, Reverse curse 1 and 2, minor warmup and yoga.
Of course during times where we have an increased schedule the time will go up, but shouldn't surpass 3 hours.
You can add mantras and planetary squares to your routine if you want. How much of your free time you want to spend is on you. But 8 hours is more than enough.
Unless that 8 hours is your sleep schedule, which you could sleep 6 and do your meditations in that 2 hour span.