Premixing and sending mixed coins are two different phases for DASH.
Sending premixed coins is instant.
Mixing your balance can be done whenever you want. Speed will pickup with time, as more people use mixing and there is greater "availability" to mix with. At that point, when a lot of people are mixing, bloat and fees will be the issue. I think we already had a glimpse of the future when premixing with multiple rounds was implemented and the network got congested from all the people who were waiting to mix their coins for the first time. IIRC the fees were bumped a bit, or it was suggested that txs would go through faster with a fee - something like that.
The concept of PREMIXING is like me saying
ME: Hey AlexGR, remember that money you owe me.... can you give me some cash to settle that debt so I can go and buy a FLUFFYPONY?
AlexGR: Sure ....let me go to my wallet and get some.
......10 minutes goes by......
Me: AlexGR, what's taking so long?
AlexGR: Hold on I'm premixing my bills because the cash won't let me give it to you until it is PREMIXED properly.
Me: Oh....oh okay How much longer?
AlexGR: Any minute now...
...30 min goes by....
Me: Dude, what is going on?
AlexGR: Sorry man this is taking so long. I knew I should have PREMIXED my cash in advance. SHIT.
Me: how much longer?
AlexGR: I guess maybe another 30 min?
Me: Okay I'll wait
....35 min goes by....
Me: is it done PREMIXING yet?
AlexGR: No. It shouldn't be long...
Me: Okay dude just call me when it is done. Oh and next time PREMIX your shit before hand so when I come to collect my money you aren't wasting my time!
