Beta blockers 2 or 3 hours before sounds good, gives them enough time to kick in.
Benzos might not take full effect in such a short time as 20min. I'd break up my benzo dose, depending on how much I had. I'd take a small dose 5 or 6 hours before, maybe 1 or 2 mg. Just to loosin' you up. Then I'd take a bigger dose 1 hour before taking SN, upwards of 10mg. 1 hour gives sufficient time for the benzos to kick in. Then I'd take take the rest of my benzos in with my SN. For good measure.
Yes I suppose it won't hurt to move them earlier to get the full effects although they start to work after 30 minutes.
Updated schedule
Day 1 Medication and Dose
08:00hrs 1 X 10mg Metoclopramide
16:00hrs 1 X 10mg Metoclopramide
24:00hrs 1 X 10mg Metoclopramide
Day 2 Fast, Medication and Dose
08:00hrs 1 X 10mg Metoclopramide
16:00hrs 1 X 10mg Metoclopramide
22:30hrs 1 X 100mg Propranolol
22:45hrs 1 X 1000mg of Paracetamol
23:00hrs 3 X 10mg Metoclopramide (30mg in total)
23:15hrs 4 X 75mg Ranitidine (Crushed Pills)
23:45hrs 1 X 20mg Diazepam
24:00hrs 1 X Mix 30g SN in 50ml Water
24:05hrs 1 X Last Cigarette, roll up of Golden Virginia tobacco
24:15hrs 1 X SN Drink
Cheers Geo