Therefore, I believe delaying investing in Bitcoin until we have discretionary funds is a bad idea.
Where did you get this idea from? So if you think it's a bad idea to delay investing in bitcoin till you come up with discretionary income, what money do you now want to invest in bitcoin with? Is it the money ment for your family essentials? Or the money needed to run your day to day life? Well it's only advisable to invest in bitcoin with discretionary income. If you don't have discretionary income it's not advisable to use money for other essentials to invest in bitcoin. So delaying investing till you are are able to come up with discretionary income is not a bad idea.
He surely doesn't understand financial management and Bitcoin investors who have such mindset cannot sustain DCA method of accumulation. If he doesn't have discretionary funds I wonder from which funds that he will be taking out money to buy Bitcoin. I guess that he doesn't know that total income - basic expenses = discretionary funds. Therefore if you don't have discretionary funds it'll means that all your income goes into basic expenses.
Discretionary funds are for expenses that you can do out of your own discretion, it means they are not among the expenses that are on your must do list like food. You don't need Bitcoin investment to survive day by day but you must eat so you need food to survive day by day. Food falls under must do expenses so it's a primary need while Bitcoin investment is a secondary need that you can decide to do out of your discretion.