diff --git a/pygmt/src/timestamp.py b/pygmt/src/timestamp.py
index 6ed3ee39fb4..96c816a67d9 100644
--- a/pygmt/src/timestamp.py
+++ b/pygmt/src/timestamp.py
@@ -1,65 +1,69 @@
 """
 timestamp - Plot the GMT timestamp logo.
 """
+from __future__ import annotations
+
 import warnings
+from typing import TYPE_CHECKING
 
 from packaging.version import Version
 from pygmt.clib import Session, __gmt_version__
 from pygmt.helpers import build_arg_string, kwargs_to_strings
 
+if TYPE_CHECKING:
+    from collections.abc import Sequence
+
+
 __doctest_skip__ = ["timestamp"]
 
 
 @kwargs_to_strings(offset="sequence")
 def timestamp(
     self,
-    text=None,
-    label=None,
-    justification="BL",
-    offset=("-54p", "-54p"),
-    font="Helvetica,black",
-    timefmt="%Y %b %d %H:%M:%S",
-):
+    text: str | None = None,
+    label: str | None = None,
+    justification: str = "BL",
+    offset: float | str | Sequence[float | str] = ("-54p", "-54p"),
+    font: str = "Helvetica,black",
+    timefmt: str = "%Y %b %d %H:%M:%S",
+) -> None:
     r"""
     Plot the GMT timestamp logo.
 
-    Add the GMT timestamp logo with an optional label at the bottom-left corner
-    of a plot with an offset of ``("-54p", "-54p")``. The timestamp will be
-    in the locale set by the environment variable **TZ** (generally local time
-    but can be changed via ``os.environ["TZ"]``) and its format is controlled
-    by the ``timefmt`` parameter. It can also be replaced with any custom
-    text string using the ``text`` parameter.
+    Add the GMT timestamp logo with an optional label at the bottom-left corner of a
+    plot with an offset of ``("-54p", "-54p")``. The timestamp will be in the locale set
+    by the environment variable **TZ** (generally local time but can be changed via
+    ``os.environ["TZ"]``) and its format is controlled by the ``timefmt`` parameter. It
+    can also be replaced with any custom text string using the ``text`` parameter.
 
     Parameters
     ----------
-    text : None or str
-        If ``None``, the current UNIX timestamp is shown in the GMT timestamp
-        logo. Set this parameter to replace the UNIX timestamp with a custom
-        text string instead. The text must be no longer than 64 characters.
-    label : None or str
+    text
+        If ``None``, the current UNIX timestamp is shown in the GMT timestamp logo. Set
+        this parameter to replace the UNIX timestamp with a custom text string instead.
+        The text must be no longer than 64 characters.
+    label
         The text string shown after the GMT timestamp logo.
-    justification : str
-        Justification of the timestamp box relative to the plot's bottom-left
-        corner (i.e., the plot origin). The *justification* is a two-character
-        code that is a combination of a horizontal (**L**\ (eft),
-        **C**\ (enter), or **R**\ (ight)) and a vertical (**T**\ (op),
-        **M**\ (iddle), or **B**\ (ottom)) code. For example,
-        ``justification="TL"`` means choosing the **T**\ op **L**\ eft point of
-        the timestamp as the anchor point.
-    offset : str or list
-        *offset* or [*offset_x*, *offset_y*].
-        Offset the anchor point of the timestamp box by *offset_x* and
-        *offset_y*. If a single value *offset* is given, *offset_y* =
-        *offset_x* = *offset*.
-    font : str
-        Font of the timestamp and the optional label. Since the GMT logo has a
-        fixed height, the font sizes are fixed to be 8-point for the timestamp
-        and 7-point for the label. The parameter can't change the font color
-        for GMT<=6.4.0, only the font style.
-    timefmt : str
-        Format string for the UNIX timestamp. The format string is parsed by
-        the C function ``strftime``, so that virtually any text can be used
-        (even not containing any time information).
+    justification
+        Justification of the timestamp box relative to the plot's bottom-left corner
+        (i.e., the plot origin). The *justification* is a two-character code that is a
+        combination of a horizontal (**L**\ (eft), **C**\ (enter), or **R**\ (ight)) and
+        a vertical (**T**\ (op), **M**\ (iddle), or **B**\ (ottom)) code. For example,
+        ``justification="TL"`` means choosing the **T**\ op **L**\ eft point of the
+        timestamp as the anchor point.
+    offset
+        *offset* or (*offset_x*, *offset_y*).
+        Offset the anchor point of the timestamp box by *offset_x* and *offset_y*. If a
+        single value *offset* is given, *offset_y* = *offset_x* = *offset*.
+    font
+        Font of the timestamp and the optional label. Since the GMT logo has a fixed
+        height, the font sizes are fixed to be 8-point for the timestamp and 7-point for
+        the label. The parameter can't change the font color for GMT<=6.4.0, only the
+        font style.
+    timefmt
+        Format string for the UNIX timestamp. The format string is parsed by the C
+        function ``strftime``, so that virtually any text can be used (even not
+        containing any time information).
 
     Examples
     --------
@@ -79,7 +83,7 @@ def timestamp(
     self._preprocess()
 
     # Build the options passed to the "plot" module
-    kwdict = {"T": True, "U": ""}
+    kwdict: dict = {"T": True, "U": ""}
     if label is not None:
         kwdict["U"] += f"{label}"
     kwdict["U"] += f"+j{justification}"