my dryer runs and heats up,but the timer doesnt move,i have to push the start button and it will run forever.It will dry the clothes but I have to check on it or it will really get them hot.Is this a problem with timer or other things.

yes , that is the correct model number.

Here is your parts
Model REX5634KQ1

Here is a tech sheet
https://www.servicematters.com/docs/wiring/Wiring%20Sheet%20-%208528187.pdf

Try timed dry. Now does the timer advance?

If it does the the following may apply.
Take a look at the timing chart, you will see that timed and auto use different timer contacts re: TM-OR or TM-WB.
In timed dry the timer motor gets power direct from 120 volts (Neutral to L1)
In auto timer motor only gets power when the heating elements shuts off. This puts L2 voltage on the left side of the element, the Resistor drops the 240 down so it does not blow the timer motor. If the element never shuts off then the timer will not advance.

Most probable cause is a grounded element.
Unplug the unit.
Remove wires from the element.
Check resistance between element connectors, should be approx 10 ohms.
Check each connector to ground should be open (infinite resistance).

If you do not have a meter, inspect the element visually. You may be able to see where it is touching the case or a scorch mark where it has touched the case.

Another possibility would be the inline timer resistor or the operating thermostat.
Could also be the timer as Kayacrzy said