Does gravity exist at all times?

Yes and no.

Only when it springs into awareness. But on the other hand, it's always there. It's like your heartbeat. When you measure it, it's there—or it isn't—but the process is always there until it isn't.

When you measure a heartbeat, it is never "there" in any single, specific state. Yet over time, it is always there. The more closely you examine something, the less you may find.