Here, both sentences indicate a future event.
What is the difference between the two sentences?
The meeting starts at 5 o'clock.
The meeting will start at 5 o'clock.
Is the first sentence grammatically correct?
Will is not compulsory for all future events.
The meeting starts at 5 O'clock
The meeting will start at 5 O' clock
Both are correct and may mean almost the same.
But if you sayI think the meeting will start at 5 O'clock is common.
*I think the meeting starts at 5 O' clock is less common
There are many ways of expresing future time without will or shall
I am going home tomorrow.( future time)
I am going to meet my friend tomorrow.(future time
My father retires next year ( future time)
I have to submit my report tomorrow( future time)
If you went to Mumbai, when would you come back?( future time)
These are some of the examples only.