Appear when grandpa is out of bed (3-2)
I believe the answer is:
pop-up
'appear' is the definition.
(popping up is a kind of appearing)
'grandpa is out of bed' is the wordplay.
'grandpa' becomes 'pop' (I can't explain this - if you can you should give a lot more credence to this answer).
'is out of bed' becomes 'up' (synonyms).
'pop'+'up'='POP-UP'
'when' is the link.
Can you help me to learn more?
(Other definitions for pop-up that I've seen before include "Unrequested browser window" , "(Of toaster) automatically ejecting" , "opening quickly but temporarily" , "Three-D picture in book" , "Like many electric toasters" .)