Dear one,
Reading all of the Diamond Cutter Sutra every day would be very good, but if you cannot finish it, read some every day. You will collect unbelievable merit and purification and be able to realize emptiness and attain enlightenment, with the motivation to liberate and lead all sentient beings to enlightenment.

It comes out good for you to do all three—meditation, study and service—but, of course, you need to meditate on the lam-rim all the time.

Concerning the lam-rim meditation sections and times, work through them for months and years (not just hours or days) until you have realizations that are stable. If you do not gain the realization, practice the meditations again and again until you generate renunciation of this life and future lives, and bodhicitta. The three go together like that. However, do a little meditation on emptiness every day, even if it is only five minutes, so that before you die, you will have the realization.

Guru yoga meditation is the root of the path, and you need to gain a realization that is stable for months and years, seeing all the gurus as Buddha and all the buddhas as the guru. How much meditation you do is up to you. Then work to generate the three realizations—renunciation of this life and future lives, and bodhicitta. Depending on how much you can realize bodhicitta, you will gain lots of imprints.

Do the preliminary practices with the lam-rim as your motivation. When you are doing lam-rim retreat, also do the preliminary practices. In the morning do Guru Puja, refuge, bodhicitta, the four immeasurables, the seven-limb practice and the short mandala offering. Do all these practices with meditation, not just prayer. Think: “I and all sentient beings up until now are suffering because we have no realizations, and in the future it will be the same. Therefore, I will do lam-rim meditation for suffering sentient beings generally, then for the beings in each of the realms. This lam-rim meditation subject (that I am going to meditate on) is for gaining enlightenment, for the benefit of all my kind mother sentient beings.”

Even when doing a deity retreat, you also need to do lam-rim meditation, prostrations, etc, at that time.