Best Guess.  
Answer depends on how fast new blocks are found.

After Block # 2102400 , Mint will start 10% rate.
Current  ~ # 1892244 ,

If Mint average 3 blocks per minute 3 blocks * 60 minutes =180 blocks per hour
180 blocks *24 hours = 4320 per day
2102400-1892244= 210156 blocks until change
210156 blocks /4320 blocks per day= 48 days

However if Mint average only 2 blocks per minute , then
2 blocks * 60 minutes =120 blocks per hour
120 blocks *24 hours = 2880 blocks per day
2102400-1892244= 210156 blocks until change
210156 blocks /2880 blocks per day= 72.9 days

So you are looking at the change happening somewhere between 48 & 72.9 days from now.
But the block # the change will occur at is #2102400 .

 

FYI:
Final 5% rate starts at block #3153600.