Don't use Durations for calculating relative times #321

Job	Run time
cargo fmt --all -- --check	10s
cargo clippy -- -D warnings (ubuntu-latest)	11s
Code Coverage (ubuntu-latest, unix)	1m 39s
cargo check (ubuntu-latest)	23s
cargo clippy -- -D warnings (macOS-latest)	10s
Code Coverage (macos-latest, macos)	1m 36s
cargo check (macOS-latest)	12s
Run the fuzzers	2m 26s
cargo clippy -- -D warnings (windows-latest)	1m 49s
Code Coverage (windows-latest, windows)	4m 11s
cargo check (windows-latest)	1m 7s
cargo test (ubuntu-latest)	12s
cargo test (macOS-latest)	15s
cargo test (windows-latest)	2m 1s
	16m 22s

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