There's no single universally "correct" time for a massage, but timing does change the experience in genuinely useful ways depending on what you're going in for.
Morning sessions
A morning massage can help ease overnight stiffness and set a calmer tone for the day, particularly if you tend to wake up tight through the neck and shoulders. The trade-off is that a deep, very relaxing session might leave you feeling a little too loose and unfocused to dive straight into demanding work immediately afterward.
Midday / lunch-break sessions
Shorter, focused sessions — head, neck and shoulder, or foot reflexology — fit naturally into a lunch break and work well as a reset partway through the day, without requiring the wind-down time a longer session needs.
Evening sessions
For general relaxation and better sleep, evening tends to be the strongest choice — there's nothing demanding scheduled right after, and the calming effect on the nervous system has time to carry through into the night rather than getting immediately undone by a stressful afternoon.
What matters more than the clock
Booking a time when you're not rushing in from somewhere stressful, and don't have to rush out immediately afterward, matters more than the specific hour on the clock. A technically "ideal" evening slot squeezed between two stressful commitments will do less for you than an average midday session with a genuinely unhurried ten minutes on either side.
A practical suggestion
If you're building massage into a regular routine, evening slots generally work best for full-body relaxation sessions, while shorter midday sessions suit ongoing maintenance for desk-related tension. Match the session length and timing to what you actually need that day, rather than defaulting to whatever slot happens to be free.