Shepard knows that:
1) Reapers wipe out the Protheans
2) Saren wants to bring them back
3) Reapers are a threat to every specie in the Galaxy
He doesn't know when the clock will hit zero, but he should know that every moment spent not pursuing Saren makes Saren closer to succeeding, because there is no reason to assume Saren will sit idly and wait for Shepard to deal with Geth incursions, Rogue VI, lost data module on monkey colony or Dr. Saleon.
If this was real instead of a video game scenario, Shepard would be a complete idiot if he'd spend one minute doing anything but going after Saren.
There are two different things going on and to defend your argument you are combining the two.
1. Motivation to do a thing: how powerful a reason to act is
2. Urgency: Speed at which the thing needs to be done
Loc 1: Therum, Shepard rescues Benezia's daughter Liara T'Soni, who joins Shepard's squad;
she provides Shepard with better understanding of the vision from the beacon.
Loc 2: Feros,
Shepard acquires the ability to comprehend and interpret the images seen in the vision from a former subordinate of Benezia, and learns that Saren's flagship, Sovereign, possesses unique mind-control capabilities.
Loc 3: On the world of Noveria, Shepard tracks down and defeats Benezia,
who reveals that she and Saren are being indoctrinated by Sovereign.
Loc 4: Meanwhile, the Council informs Shepard that a salarian infiltration unit has uncovered Saren's main base on Virmire.
Sovereign reveals that the Reapers remain outside the galaxy waiting for organic life to develop and discover the Mass Relays
Loc 5: On the
Normandy, Liara pinpoints the Conduit's location: a Prothean world known as Ilos.
((massively important ticking clock starts))
Beginning: MC knows there is a potential vague threat (something wiped out protheans) - very bad. Big motivator. Saren somehow wants this information and has gone rogue. Motivation: High. Clock: N/A as no idea when events occur or what is really goign on. Sheppard barely understands the threat or even what a reaper is.
Counterpoint: Saren believed to be working with Geth. Powerful species and powerful ally. Sheppard has big MOTIVATOR to power up ship and get allies as he's going against someone who kicked butt one of the major races.
Step 2: sheppard understands a little better. vision plus sarens ship a little more (MC learns the cycle of destruction period and could be comming up on it again ((but not exact numbers)) still no idea where to go to resolve issue, just places to go for.. maybe.. more info
Step 3: MC learns saren is being controlled by the ship (clock still not ticking fast) MC still doent know where to go
Step 4: Has NOTHING to do with reapers.... but there you happen yto learn more information on the nature of the threat.. ship is a reaper and not a ship , what reapers do. Motivation increases. BUT - reapers are outside of the galaxy and would need to fly into galaxy ((space travel takes time))
Step 5: Motivation plus the danger being imminent and its nature is revealed. HUGE motivator (what happens if dont, plus must do this NOW kicks in))
A VERY WELL DONE ticking clock.
There is a motivator to do thing.. but the clock doesn't truly kick in until near the end. Allowing other things to occur (assembling your fragging CREW for example..!!!!!!))
"Shepard would be a complete idiot if he'd spend one minute doing anything but going after Saren."
Well.. if sheppard didnt take some time to assemble a crew he would not have learned about the threat (stage 2 - lliara), and would have been strongly hindered in other things.. no Garris.. no Rex.. no Tali (sheppard is an idiot conformed??)
The sun burning out/nova is a HUGE deal..... when it goes out makes it urgent/not urgent
asteroid hitting earth.. big deal.... when it might hit puts things into how urgent it is
I just LOVE people trying to tear down GREAT RPGs of the past in an attempt to make everything a binary ((everything is either linear or every game ignores a ticking clock))
Has ANYONE notices they ignored EVERY OTHER example I raised previously.... RDR2 for example? Decently done open world game in many eyes.. fallout games... W3... and time and again claim either you have a ticking clock you must ignore.. or be completely linear.
to make excuses for the three weeks and you're dead ticking clock but never mind sleep 365 days straight in your room and there is... NO CHANGE!!