如果函数保留其参数，这似乎可以工作：

It seems to work if the function holds its arguments:

tod := Mod[AbsoluteTime[], 86400]
SetAttributes[f, HoldAll];
f[x_: tod] := x

In [23]：= f []

In[23]:= f[]

Out [23] = 47628.994048

Out[23]= 47628.994048

In [24]：= f []

In[24]:= f[]

Out [24] = 47629.048193

Out[24]= 47629.048193

或者您可以使用以下结构代替默认值：

Or you can use a construction like the following instead of a default value:

g[] := g[Mod[AbsoluteTime[], 86400]]
g[x_] := x

输入[27]：= g []

In[27]:= g[]

输出[27] = 47706.496195

Out[27]= 47706.496195

In [28]：= g []

In[28]:= g[]

Out [28] = 47707.842012

Out[28]= 47707.842012