This would be possible if the person is earning way higher than $60k per year or luckily Bitcoin price drops down to $50k or they would have to increase the yearly intervals they have set to accumulate the 4.5 Bitcoin.
I am not going to presume that the bitcoin price is going to drop... sure it might, but we should not be making our plans based on things that are out of our control.. Yet, each of us should be able to figure out how much of our income that we can put into bitcoin and then therefore how much bitcoin we might speculate that we are able to accumulate through our various accumulation strategies.
In addition, the presumably possibility that price will drop is a 50/50 chance but however, focusing on price drop to accumulate is basically if not the same thing with wasting to try to find the best entry point. hence it's more of a better opinion to figure out how much you're willing to sacrifice for bitcoin within your discretionary income. if we have enough it's even more advisable to buy aggressively as long as we can afford it without tempering with our daily expenses which will lead to deeping hands into our investments.