If they're all the same format (or possibly a sufficiently small number of formats), you may be able to use strptime. If you can get something that just hits the C func, it may be quite fast (and even if it doesn't, being able to specify a format rather than call a DWIM interpretation function should be faster anyway).
I see a POSIX::strptime that seems like it may thunk straight through to libc's implementation. DateTime::Format::Strptime looks like a perl reimplementation, so may be slower (but probably more portable, if your system's strptime is broken).
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