Understood. However the question is, how big are the extranonce and the timestamp, are they both 32 bit as well as I've assumed?
This should answer your question:
Eight bytes of extra nonce, plus the 4 bytes of "standard" nonce allow miners to explore a total 296 (8 followed by 28 zeros) possibilities per second without having to modify the timestamp. If, in the future, miners could run through all these possibilities, they could then modify the timestamp. There is also more space in the coinbase script for future expansion of the extra nonce space.
Note that the extra nonce is not part of the protocol, so really it can be any size as long as it fits in the coinbase transaction. The time stamp is 32 bits.