Assuming that the stress of your unusual situation has elevated your pulse rate by an unknown amount, desynced your period (if you are female), or any other natural time measurement.

We can calculate the period of a pendulum as 2 pi SQRT(L/g).

So if we know L and g, we have our clock.

And fortunately, we can calculate g if we have a ruler.

Gentlemen, lets admit, we've all measured 'it' and know exactly how long 'it' is. Don't forget that self measurements typically overestimate by an inch or so.

Ladies, (to continue my theme of being sexist), probably know your measurements as appropriate to fit clothing, find some string-like material that you can wrap round your waist for a calibrated ruler. In fact, just use that string as the pendulum.

Now, we need to calculate g.

The best bet will be some sort of projectile motion. Jumping, spitting, peeing (yes, this post went rapidly downhill), throwing a rock could all be used to determine a total distance travelled by a projectile thrown horizontally using:

d = \frac{v \cos \theta}{g} \left( v \sin \theta + \sqrt{v^2 \sin^2 \theta + 2gy_0} \right)

Of course, you will have to know the distance that one of these projectiles traveled on Earth in order to calculated launch velocity (and then use that launch velocity and the distance on the new world to calculate g), so I hope you know how far you can throw/excrete something.

Plug in our calculated L and g into the pendulum formula and we have a working pendulum. From there, it's some simply gears to get us a clock and calendar.

This avoids us needing to directly measure/assume anything to do with speed or time, because those are hard.

Assuming that the stress of your unusual situation has elevated your pulse rate by an unknown amount, desynced your period (if you are female), or any other natural time measurement.

We can calculate the period of a pendulum as 2 pi SQRT(L/g).

So if we know L and g, we have our clock.

And fortunately, we can calculate g if we have a ruler.

Gentlemen, lets admit, we've all measured 'it' and know exactly how long 'it' is. Don't forget that self measurements typically overestimate by an inch or so.

Ladies, (to continue my theme of being sexist), probably know your measurements as appropriate to fit clothing, find some string-like material that you can wrap round your waist for a calibrated ruler. In fact, just use that string as the pendulum.

Now, we need to calculate g.

The best bet will be some sort of projectile motion. Jumping, spitting, peeing (yes, this post went rapidly downhill), throwing a rock could all be used to determine a total distance travelled by a projectile thrown horizontally using:

$d = \frac{v \cos \theta}{g} \left( v \sin \theta + \sqrt{v^2 \sin^2 \theta + 2gy_0} \right) $

Of course, you will have to know the distance that one of these projectiles traveled on Earth in order to calculated launch velocity (and then use that launch velocity and the distance on the new world to calculate g), so I hope you know how far you can throw/excrete something.

Plug in our calculated L and g into the pendulum formula and we have a working pendulum. From there, it's some simply gears to get us a clock and calendar.

This avoids us needing to directly measure/assume anything to do with speed or time, because those are hard.