Is there a specific time in the day wher

Short answer: it depends which "sign" you mean — a sign that tracks a *time of day* exists in astrology (the rising sign), but tarot has no such thing at all.

If you mean zodiac signs:

• Rising sign (ascendant) — this is the one that changes *during* a day. The eastern horizon sweeps through the zodiac at roughly 15° per hour, so a 30° sign takes about two hours. That's why two people born the same day can have different rising signs, and why birth time matters for a chart but not for a Sun sign.
• Sun sign — doesn't move within a day. It flips at one instant per year, at a slightly different clock time each year depending on your time zone.
• Moon sign — moves too slowly for that; it changes roughly every 2½ days.

If you mean the Chinese system: time of day is built in directly — the 12 double-hours (时辰, 子丑寅卯…), one every two hours. That's the closest thing to "a time of day where the sign changes."

If you mean tarot: no. A card doesn't belong to an hour. The spreading of cards on a clock-face that you may have seen is a folk practice with roots outside Rider–Waite; in a normal RWS reading, time enters only as "right now," and the meaning lives in the position and the cards in it, not the clock.

One honest limit: all of the above is symbolic tradition, not physics — nothing measurable changes at 11:00 or 15:00.

If it's your own chart you're after (a specific sign at a specific hour for you), tell me your birth date, time, and city and I'll say which of these actually applies to you.