My initial interpretation of Trump's post was that Russia would supply a TOTAL of 3 million tons "within a short period". But others have pointed out that he may have meant 4.8M tons total. Also, US daily consumption is nearer 4M bbl/day. So 4.8M tons = 36M barrels = 9 days.
🤔 MATH
Russia says it will supply about three million tons of diesel into global markets between now and some indeterminate time in the future.
3M tons = ~24M barrels.
The US consumes ~5M barrels each day.
So Russia has agreed to sell 5 days worth of US diesel consumption.