@Raghu1986 In base game and seafarers development cards can be bought by clicking on the card stack on the bottom of the game board (provided you have sufficient resources). In cities and Knights cards can´t be bought you have to build city improvements via the trade resources the dice will determine if you get a card or not (depending on the level of city improvement you have built) you can also check out the in game almanac for further info.
A very simple way to see if the timer works properly would be to actually display the timer on screen and sync it every 5 seconds. Something the players have asked for since the timer was created. But no, the developers are randomly updating each feature very small steps at a time.