Some of the answers are close, but no cigar. The main reason for the time delay is the offline authentication of the chip, combined with generation of the ARQC cryptogram. Additionally the EMV protocol is very chatty if there are multiple applications on the chip card, although the latency involved in the customer interaction far outweighs the protocol timings.

As mentioned in many comments online transactions will be an order of magnitude slower, as they need to be sent to the issuer, have their cryptogram verified and the challenge response returned if the card does host authentication - which most do these days.

The entry mode generally does not determine how a transaction is authorised - chip, PayPass (NFC) and stripe can either be off or online. In fact stripe transactions are invariably online unless you want your business to be overrun with fraudsters. One of the prime reasons in the early days of EMV was to have it so safe that offline transactions were fraud proof - or close to. Naturally this noble goal was shot full of holes the moment real fraudsters got to it. However, the card is personalised with various limits and counters and with the possibility of using an offline PIN, which combined with the static authentication does give reasonable protection for low value offline transactions. Fun fact - in the initial spec this offline PIN was communicated between the terminal and the card in the clear. What could possibly go wrong :-). These days it is encrypted.

Anyhow enough blather - hopefully this has given a bit of insight.