How quickly do landslides occur?
A historic yet well observed landslide in the East Kootenays of British Columbia took approximately 100 seconds to settle, Frank Slide.  The slides at Sierra Leone and the Philippines that you mentioned are a different type of slide made of mud and other unconsolidated materials.  I cannot find any information on them but I have witness a few slides in my previous forestry work.  From my observations a slide can occur in 10s of seconds, quick slump flowing fast enough that one cannot escape if you were to be in the path, the one I witnessed took a truck off the road and about 150 meters down a shallow bank the people in the truck escaped but we lost the truck.  They also can occur very slowly, we had an area that due to changes in the drainage up slope started slumping.  The slumping started in March but didn't stop until September.  In the case of the slow slide/slump it took a hectare of forest and slowly moved it down slope and across a road very slowly.  Often the speed of the slide seems to be affected by the amount of water in the soil.  The fastest being the closest to be categorized as a debris flow rather than a slide, the other factor is the steepness of the slope, the steeper falling faster.