Hi Mega. I'd suggest the following changes:
1: Starting out at 25-50 is a bit low for a 20,000 starting stack if you're just doing a 2-day event, IMO. That's starting stack=400 times the BB... I'd start out w/ higher blinds.
2: Some of your blind raising is a bit heavy, for example, when you raise from 400 to 600 (50% increase) and from 2k to 3k (50% incr) to 4k (33% incr) to 6k (50% incr again), then from 20k to 30k and 40k to 60k. Those are uncomfortably high-percentage blind increments for a classy event, I'd suggest making them a little less steep, never exceeding 25% or so increase per increment is alot more comfortable for players to play their best poker without feeling too much blind pressure
3: Introducing an ante at level 6 is a bit soon and a 25 ante given 20,000 starting stacks is just nothing. I'd start the antes a bit later, say when the BB hits 800 or 1000, and start the antes at 100 at that time. I DO like your ante % which you're keeping around plus or minus 10% of your BB, that's good, just start it a bit later at a higher BB level.
4: Your 40 to 50 time increment is fine. If you're tight for time you could start your 50's a bit later (say at level 15). You could also even do 35's to start for a few rounds, then 40's, then 45's, then 50's. Anything so that you don't have to push the blinds so much as I mentioned in item #2.
SO, with the above in mind, I'd suggest something more along these lines, given a 20k starting stack:
50-100. The average stack is 200 times the BB, that's very comfortable.
75-150.
100-200. After this, try to limit each increment to plus or minus 25% ... 125/250, 150/300, 200/400 (I know that's 33%), 250/500, 300/600, 350/700, 400/800, 500/1000 (Start Antes @100) 600/1200, 800/1600, 1000/2000, 1200/2400, 1500/3000, 2000/4000 (a 33% jump!), 2500/5000, 3000/6000 and so on.... Hope this helps, let us know what structure you finally come up with.