2.5 years to halve the reserves, the spend cannot be linear and I also don't think they need to get to zero to have a collapse.

... The economy is being funded by the cash reserves, which increases inflation, which leads to another round of interest rate hikes to combat inflation, which makes it harder to borrow money, which is necessary for economic growth. Eventually, the cash reserves will run out. It took 2.5 years to deplete half the Russian reserves. Russia withdrew $37 billion to cover deficits in December 2022. It withdrew $20 billion to cover deficits in December 2023. It only has $54 billion left.