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Plainly, evaluating $10^{19}$ positions is not going to be feasible in 7200 seconds. But if you use alpha-beta to prune the search tree and have perfect move ordering you can get that down to around $10^{10}$, a number that looks much more reasonable given that chess engines on PC hardware can do a couple million nodes per second easily. Since alpha-beta ...
It's a straightforward Fermi estimate: if you spend one microsecond of CPU time on each node of the tree, and if you visit $9^{20}$ nodes of the tree, then the computation will take about $9^{20} \times 10^{-6}$ CPU-seconds. If you have 10 CPUs, divide by 10 to get the elapsed time. I'll let you plug that into a calculator and formulate the appropriate ...