third time I am writing

[azz]

Can one say
a. This is the third time I have written to you.
b. This is the third time I am writing to you.

c. This is the third time I have been here.
d. This is the third time I am here.
?

Does changing the tense change the meaning?

Many thanks.

 

[probus]

In mainstream English a. and c. are correct, and b. and d. are not. But b. and d. are commonly heard in Indian English.