There's a good rule of thumb when it comes to a question of "what do I do after I lob".
But before, there is no question "should I take the net", you always have to take the net \_if\_ you have opportunity. It's padel essentials and 101 -- create opportunity, take the net, win the point, rinse-repeat, win the match.
So, the thing. After lob, your signal to take the net is when you see their backs. Only after you rush and take the net. If you don't see their backs, they still maintain the attack and you should move to "active" defence.
(Active defense - a waiting position for you and your partner to either a) rush and take the net b) return shot and take the net c) go back to normal defence, i.e. move back. Defending player, i.e. the one that has biggest angle opened on him moves closer to fence, his partner covering center)
So yeah. Hit the lob, move a bit up to service line, then either rush to net if you had seen their backs or starting jump and react on them maintaining their attack.