=IIf(t1 > IIf(t2 > t3, t2, t3), t1, IIf(t2 > t3, t2, t3))

That kind of expression gets very messy very quickly, so
it's almost always better to create a function to do the
calculation:

Public Function MaxOfList(ParamArray vValues() As Variant)
As Variant
Dim vX As Variant

   MaxOfList = vValues(0)
   For Each vX In vValues
       If vX >= Nz(MaxOfList, vX) Then MaxOfList = vX
   Next vX
End Function