Would you rather have $10 now, or $10 in a month? Regardless of how you would use the $10, having it now is preferable. It count be invested. It could pay bills. It could buy a nice cup of coffee and a donut. None of your choices would affect the time reference.
Opportunity costs are easily understood if you have to fund projects and make hard budget choices, but the more important application for many conversations is part of Bastiat's broken window fallacy in my opinion.
Some people condemn both lending/borrowing at interest and investing for interest. Like you said, inflation distorts future value even more, but time preference and risk plus wider market supply and demand for investment funds should rationally be part of the price calculation of our consideration.