Minecraft wiki entry for Advanced_redstone_circuits, associated text: Because of the delay that the redstone torch adds, the delay of the initial repeater, the one that stays unlocked, must be increased to 2 ticks.
The data from the timer will be preserved.
Because the repeaters will still be powered when the timer is used again, the circuit must be obstructed between uses in order to unlock the repeaters. To do this mine the redstone torch, wait for all of the repeaters to deactivate, and put the redstone torch back.