Target group by hours after creation

[yuvals]

Is it possible to send action based email when a field in the recipient data changed? and not by clicking on a link or filling out form?

for example: my customers can register to my mailing list in several ways, and i want to send a welcome email few hours after they register.
what is the best way to accomplish this? (i'm thinking of when the registration date changes but couldn't find a way to do this).

Thanks.