I really agree with you that there is no fixed amount or price when it comes to DCA, it all depends on personal interest or choices in which you can eventually be able to afford without having a break down in your daily income or monthly salary,
Even if you can use any amount to invest at any time of your DCA but it should be within your discretionary income and also, making an investment plan for your income is very important such that you can focus more on your most important needs in order for you to have enough discretionary amount to invest. On a normal context of the DCA, it is supposed to be about investing same amount of bitcoins but the reason why we don't need to be so strick about the fixed amount is for a stress free investment without having to be struggling to meet up with the fixed amount at every time of your DCAing.
buying of Bitcoin is what will take time and years for the dip to happen.
I don't even get what you're trying to say here because a DIP can happen at any time so which one is taking time and years before a DIP can happen. Let me make it clear to you, a DIP doesn't mean that the price of bitcoin must fall drastically before we can refer to it as a DIP, ordinarily buying bitcoins at lesser price than the previous price you bought can be said to be a DIP price.