I was in India over the summer; posted the application on a Tuesday and it was returned by Friday (by post) but the website does state to allow two weeks to be sure.
Looking at it states
In case of emergency or extreme urgency, visas can be granted on the day of application or the next day, if the visa officer is convinced of the genuineness of the need. In such cases , an additional visa fee (Express Visa Fee) of Euro 50 will be charged, over and above the applicable visa fee indicated above. This facility is available only to Irish passport holders.
Considering it costs €50 for the visa in the first place, it is a pretty expensive option.