1992 Volvo 240 shift lever knob

After I crank my car and it starts especially after it's been cold or first time in the morning ; I try to depress the shift lever knob on the shift lever assembly to put it in gear in drive or reverse ; but the knob doesn't move and it doesn't release the sheft lever to go in drive or reverse. I have to wait sometimes up to 15 minutes to let the car idle until it warms up and then I hear a click and the shift lever knob is then ready to depress and release the shift lever to drive or reverse. What's causing this delay and how do I get it fixed ? After the car idles for 15 some minutes i'm then able to put it in gear and it runs fine.