First swim meet in 35 years

HI there, if it's an option, you can enter NT (no time). That way, you will be seeded in the first heats and can see where you are at with your times for the next meet entry.

If you have to submit a time. Give it your best guess. I recommend timing yourself in practice to have a baseline.

Good for you!  I also had a 35 year break from swimming.  I timed myself during workouts to get an idea what entry time that I should use for each event that I wished to swim.  Obviously my time in a workout was going to be faster than in a meet but that is where I started.  One thing that I suggest is that you should get some work off the blocks if you can because the blocks looked much higher than what I remember and made me uncomfortable.  By the way my first USMS meet was in February 2016 and I am still at it.  Good luck.  

Good luck!!!  I, too, took off 30+ years and had my first meet in January.  I definitely wouldn't use my times from the past (I was a 2:05 200 IM'er back in the 80's; now it is more like 3:20).  If you are unsure, you can guess based on your workout times, or to be safe NT is a good option.