Contactless card uses the same chip and PIN module as in contact card. The difference between them is in the medium of communication with the terminal and in application selection. Contactless cards store additional cryptographic keys to authorise contactless transaction. As their keys are separate, the issuer can disable contactless payment by always rejecting contactless transaction authorisation request but still allowing contact payments. Some banks offer this opt-in feature to prevent unauthorised use of stolen contactless cards.
In contact payment, there are no time constraints. Contact card can even tell terminal to wait and call it again after some seconds and then it can do this indefinitely (21:01). Some terminals can also tolerate few seconds round trip delay (23:18) because contact cards are slow (600 bits per second (23:56) and transaction can be few bytes long).
The recommended transaction time for contactless payment is 500ms but it is not globally enforced by the issuers as terminals can itself add latency in processing. Most of the contactless payments take 330ms - 637ms and some terminals can allow max transaction time upto 52 seconds (16:30). This out of specs implementation is to maintain compatibility across card issuers and PoS manufacturers (In UK alone, there are almost 300 approved chip and PIN terminals). This is why relay attacks are successful.
However, there is a max allowed time length in Distance Bounding Protocol which combats relay attacks. Distance bounding is in the EMV contactless specification and Mastercard has taken up this defence, meaning its cards (at least) are protected.
ICC does not have an internal clock. For signal processing and I/O modes, ICC relies on clock signal provided by the terminal.
I/O line can be switched to (reception mode) receive data from the terminal or to (transmission mode) transmit data to the terminal.
EMV Book 1, 7 - Physical Transportation of Characters
During the transaction process, data is passed bi-directionally between the terminal and the ICC over the I/O line in an asynchronous half duplex manner. A clock signal is provided to the ICC by the terminal, and this shall be used to control the timing of this exchange.
ICC cannot measure the time between two command.