Should I limit the time I do metta?

Question

Metta feels great. It is unconditional love on tap. So, could there be too much of it? It is addicting.

Answer 1

No, there's no limit to practising metta. In Metta sutta it is mentioned that the one who practices this can do it anytime and anywhere.

Whether standing or walking, seated or lying down free from drowsiness, one should sustain this recollection.
Metta sutta

This is one of the four protective meditations (metta, contemplation of the Buddha, death and foulness of the body) and you won't experience side effects as in other types of meditations as well. You cannot practice breathing meditation when you are ill, like headaches and anxiety, it tends to aggravate the problem, but metta doesn't. Also, it is usually recommended to practice the four protective meditations before breathing meditation to reduce defilements.

The claim, metta meditation does not lead to wisdom is also not entirely true. In AN 11.16 sutta it is clearly stated how a metta jhana can be used to develop insight.

Then again, a monk keeps pervading the first direction with an awareness imbued with good will, likewise the second, likewise the third, likewise the fourth. Thus above, below, & all around, everywhere, in its entirety, he keeps pervading the all-encompassing cosmos with an awareness imbued with good will—abundant, expansive, immeasurable, without hostility, without ill will. He reflects on this and discerns,

‘This awareness-release through good will is fabricated & intended. Now whatever is fabricated & intended is inconstant & subject to cessation.’

Staying right there, he reaches the ending of the mental fermentations. Or, if not, then—through this very Dhamma-passion, this Dhamma-delight, and from the total wasting away of the first five Fetters—he is due to be reborn [in the Pure Abodes], there to be totally unbound, never again to return from that world.
AN11.16

Answer 2

Metta is a type of samatha (tranquility, concentration; 2nd training) practice (with a particular object: loving-kindness), so it feels good and has other benefits -- but it does not produce any insight/wisdom. It is not a criticism, it is simply not its goal (just like eating does not produce wisdom, but is still something very useful).

I've seen people doing "too much metta", as an escape from looking at negative stuff they had inside, in particular hatred they were unaware of and could not deal with. As you say that it feels addicting, be aware of attachment to those mind-states (attachment to jhanas is removed only at the moment of final enlightenment -- says the theory of 10 fetters) as much as possible. What produces insight/wisdom, and also removes negative conditions (incl. attachments), is vipassana (3rd training).

Take good care to do enough Vipassana, that's what ultimately brings more understanding about oneself and better life.

Answer 3

In the Tikaṇḍaki Sutta (A 5.144) the Buddha recommends a balance. Contemplating impermanence or the foulness of the body with regards to those objects (people) we are agreeable with, projecting metta towards objects that we find repulsive, seeing impermanence and the foulness of the body in those objects we find repulsive, and projecting metta towards those objects we find agreeable, and considering both the repulsive and agreeable with equanimity.

Tikandaki Sutta translation and comments by Piya Tan