how long does it take for an mining machine to exhaust 2^32 in minutes and what is the actual speed of mining machines?
According to the Bitcoin wiki, it refers to:


  Hash per second is an SI derived unit representing the number of double SHA-256 computations performed in one second, referred to as hash rate. It is usually symbolized as h/s (with an appropriate SI prefix).


You are correct in noting that the nonce space is quickly exhausted with modern miners.

This is solved by updating the so-called "extraNonce" in the coinbase transaction. This has the effect of changing the hash of the coinbase transaction, which in turn changes the merkle root included in the block header. This essentially provides an additional 32 bytes of nonce space, since the coinbase tx can be modified as many times as required.

Additionally, but not nearly as relevant with today's hashrate, the timestamp field of the block updates every second and allows for all nonces to be recalculated with the new timestamp as well.