OK, I'll start by saying that the blade probably hardened enough to be a usable knife.
BUT......
The metallurgy of HT is pretty specific. The steel has to cool at a rate that will miss the pearlite nose at 1000F. This can take from .5 seconds to minutes, depending on the steel type.
1084 has a pretty fast cooling curve - about 1 second to the nose.
1095 and W2/W1 are very fast, about .5 second to miss the nose, and need the fastest quenchants. Water/brine is the perfect quenchant for larger and thicker objects, but in knife blades a very fast oil like Parks #50 or Houghton K is the best choice.
O-1, 5160, 52100, and L-6 are slower, and best done with slower oils like Tough Quench, Houghton G, or Heatbath/Parks AAA.
a-2 and some other steels have cooling curves that are slow enough to quench in slow oil or in air ( if the piece is thin like a knife).
Stainless steels can take many minutes to reach the nose with no loss of hardness. That is why they can be cooled in air, which is less violent than an oil quench.
The time to drop past the nose is not to be confused with the cooling rating of quench oils, which based on a different type test. (I don't remember the exact test, but it is about cooling a specific size piece of round steel, at a specific temperature, in a specific amount of coolant, and lowering the temperature a specific number of degrees. The rating is the number of seconds it takes)
Water/Brine is about a 5 second rate.
Parks #50 is about a 7 second oil.
Houghton K and Brownell's Fast-Quench are a 7-9 second oil.
Canola and peanut oil are in the 9-10 second range.
Brownell's Tough Quench, AAA or Houghton G is a 10-13 second oil.
ATF, used motor oil, and other "garage" oils are even slower, as well as not containing the various ingredients that make quench oils good at what they do.
The cooling rate is determined by the type of quenchant and the temperature it is at. The temperature is what controls the viscosity and convection of the liquid. Fast oils are just barely able to hit the one second drop past the nose when all things are right. Almost all quench oils are at their perfect rate at 130F. Since the oil immediately heats up to a higher temp when the 1500F blade is inserted, many folks use 120F as the oil temp before the quench. Water/brine quenches work best at about 120/130F.
The exception is Parks #50, which is designed to work at room temp. 70-80F is the perfect range for #50.
If you increase or decrease the quenchant temperature from the 130F spot, you get a bell curve. The rate gets slower as you move away from the top of the bell. A 11 second oil at 130F becomes a 13 second oil at 110/150F, and a 15 second oil at 90/180F.
If you quench 1084 at room temp in canola/peanut oil, it is acting like a much slower quenchant.
1084 is a shallow hardening steel. In the thickness of a knife blade, that isn't a concern, because it hardens deep enough from both sides to be hard completely through. If the cooling rate is decreased, it may have a less hard, or unhardened core. This is actually an attribute, but is is impossible to control, so it is considered a bad thing. There may be a mix of pearlite and austenite in the martensite as well. It will be hard enough to make a serviceable blade, but won't be as good a blade as one done in Parks#50 at 120/130F would be.
To add to this, commercial oils are blended with other oils and additives that change the rate at different temperatures,These cool fast between 1500 and 900, and slower below that. They also have additives that cut smoke,burning, breakdown under heat, moisture absorption, and acidification. They are usually called "engineered oils". While canola may quench at almost the rate of Parks #W50, it won't have the usable life or continuous quality. Buying a 5 gallon pail of Parks #50 and or Houghton G is a very good use of your money. If kept in covered quench tanks and capped pails, you can likely sell them years later for half what you paid. Your canola will have to be replaced at least yearly.
