btcio: UNIX time instead of elapsed time

[voidash]

Description

use SystemTime::now().duration_since(SystemTime::UNIX_EPOCH)

Type of Change

• fix (non-breaking change which fixes an issue)

Checklist

• I have performed a self-review of my code.
• I have commented my code where necessary.
• I have updated the documentation if needed.
• My changes do not introduce new warnings.
• I have added tests that prove my changes are effective or that my feature works.
• New and existing tests pass with my changes.

Related Issues

#177

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[delbonis]

Looks good.