It is well known that "God is Love" but, is there ever a time, according to 5 point Calvinists, in the bible when God is not loving? If so, according to 5 point Calvinists, what causes God to act as such?
Yes, the God of Calvinism is loving and no, there is never a time when his actions are not loving.
The loving nature of God is, according to Calvinism and Reformed theology in general, both perfect and immutable. There is no time in which he is not loving nor action which does not display his love.
The reason many people have a problem with this is that they are using much more limited definitions of love and trying to apply them to God. A mutable fickle loving nature would indeed sometimes act out of motives other than love -- some actions would be loving, others not. As broken humans we tend to default to understanding others actions in this way, however the model does not apply to God.
God's love is both an intrinsic value and an action.
It is, however, not self contradictory. His love is not expressed in embracing both good and evil. A complete, whole, rational love that is good must also be complemented by a whole, rational and holy hatred. In order to love what is good, it must also hate what is evil. In order for God himself to be loving in Character, he must be fundamentally opposed to things that are not loving. In other words, his is not only just to punish evil, but loving to do so. It would be no love of the good and innocent to let the evil and guilty go free.
The absolutely crazy "exception" to this -- and it's technically not an exception at all because his love is consistent even in this case -- is the forgiveness and reconciliation of sinners to himself through the sacrifice of Jesus. By himself becoming subject to the curse of sin and wrath of God against evil when he himself was good, he earned the right to buy back those whom he chose from death -- to experience God's love of good as one of those good things rather than experiencing his love for good things expressed as his hatred of bad things.
Bible has depicted all God's intent as out of love for His chosen people and consequently through them to the whole of humanity .
He is always loving but this cannot be generalised universally as to force or expect Him to love what is evil and bad. Just because God is 'love' does not mean He is supposed to show love and affection to what is evil and consequently take out hell from existence and allow devil to go scot free (that is what some of us are expecting Him to do). If it is so then Devil would have won against God, hands down.
When man takes side of devil and his ways, God has to correct man to bring him back on track. Remember the saying 'doctor hurts to heal' or else there would be no cure. .