Hi @mark.sadegursky!
I tried my best but looks like we need process.hrtime() in order to make it work.
However, process module is not available as discussed here 
If this module was available, it would be possible to utilise one of external libraries such as this one to make it work by leveraging eval() function, e.g.
In pre-request:
pm.sendRequest('https://peterolson.github.io/BigInteger.js/BigInteger.min.js', (err, res) => {
if (err) {
console.log(err)
} else {
pm.environment.set('bigInt', res.text())
}
})
In test script:
eval(pm.environment.get('bigInt'))
//const loadNs = process.hrtime();
const loadMs = new Date().getTime();
const diffNs = [ 8, 886896255 ] // should really be process.hrtime(loadNs)
const value = bigInt(loadMs).times(1e6).add(bigInt(diffNs[0]).times(1e9).plus(diffNs[1])).toString();
console.log(value)
I hope you find this helpful a bit 