Timestream Navigator does not have summoning sickness.
Mana Needed
({3} magic symbol) ({U} magic symbol) available on your first turn, and ({2} magic symbol) ({U} magic symbol) ({U} magic symbol) each following turn available.
Steps
Cast
Selective Memory by paying ({3} magic symbol) ({U} magic symbol) , exiling all creature and planeswalker cards from your library.
At the beginning of your next upkeep, The Prismatic Bridge triggers.
In response, activate
Timestream Navigator by tapping it, paying ({2} magic symbol) ({U} magic symbol) ({U} magic symbol) , and putting it on the bottom of your library, taking an extra turn after this one.
Resolve The Prismatic Bridge's trigger, revealing cards from the top of your library until it reveals
Timestream Navigator and puts it onto the battlefield.
Repeat from step 2.
Notes
Timestream Navigator may instead start in your library. In this case, do not exile it with
Selective Memory, and The Prismatic Bridge will find it. This version of the combo takes an extra turn unless you have a way to grant