nb-timepicker invalid date issue

### Issue type

**I'm submitting a ...** (check one with "x")

* [ x] bug report
* [ ] feature request

### Issue description

**Current behavior:**

When I try to change time in nb-timepicker there is an error called
InvalidPipeArgument: 'Unable to convert "Invalid Date" into a date' for pipe 'e'

This occurs only when computer date in January. When I change it to February this works fine.
If we remove the default value in formBuilder this will work fine.

**Expected behavior:**

Should able to change time.

**Steps to reproduce:**

**Related code:**

```
html file

ts file
this.jobDetailsFormGroup = this.formBuilder.group({
startTime: [new Date(), [Validators.required]]
})
```

### Other information:

**npm, node, OS, Browser**
```
Node:v14.15.5, npm: 6.14.11
OS: Windows (10).
Browser: Edge

```

**Angular, Nebular**
```
"@nebular/theme": "7.0.0"
"@angular/cdk": "^11.0.0"
```