I'm trying to figure out the timing of the 3 recovery burns and the total fuel reserve needed to perform them. [Answers Inlined]
Boostback:  seconds of 3-engines at full-thrust.
Reentry:  seconds of 3-engines at full-thrust.
Landing:  seconds of 1-engine throttled between 70-100% (Merlin 1-D throttle range). They probably target somewhere between the midpoint (max margins) and higher throttle (better efficiency), so maybe 90% on average?
Merlin 1-D+ (F9FT) fuel flow rate is 270.7 kg/s.
S1: 270.7*3*30 = 24,363kg (wow)
S2: 270.7*3*20 = 16,242kg
S3: 270.7*0.90*32 = 7,796kg
Total: 48,400kg of fuel reserve (wow!).