I referenced this post: How to convert date format in golang? and have this code on the playground:
https://play.golang.org/p/oNFVlDz9JoF
But I can't seem to get it to work. I've padded the month with a 0 and still no dice. The time I'm trying to convert is 4/20/2018 9:08:34 AM and I want it in this format: 2009-04-20T21:18:44Z
NewLastDate = CDate(LastModified) 'generates 4/20/2018 9:08:34 AM
That's from a VBA script. 'LastModified' is in this format: dddd.ttttt VB/VBA format
Go time formats are interesting, you always have to put your formats in terms of (per the docs) https://golang.org/pkg/time/#Parse
01/02 03:04:05PM '06 -0700
I changed your formats a bit so you could see what is happening. I also would advise checking error returns. It also seems like time.RFC3339 is a good shorthand for what you are looking for on the output side but I may be wrong.