It takes from 5 (shortest) to almost 40 (longest) minutes for `bitcoin-cli gettxoutsetinfo` to return an _empty_ dict. I noticed this first whilst configuring the Statoshi branch of Bitcoin Core, but went back to install Bitcoin Core (git clone -b v0.11.2 https://github.com/bitcoin/bitcoin.git) to find the same results.

```
20:10 pi@raspinode:~/bin/bitcoin.orig $ bitcoin-cli gettxoutsetinfo
{
}
20:12 pi@raspinode:~/bin/bitcoin.orig $ bitcoin-cli getinfo
{
    "version" : 110200,
    "protocolversion" : 70002,
    "blocks" : 393193,
    "timeoffset" : 0,
    "connections" : 12,
    "proxy" : "",
    "difficulty" : 113354299801.47113037,
    "testnet" : false,
    "relayfee" : 0.00005000,
    "errors" : ""
}
20:17 pi@raspinode:~/bin/bitcoin.orig $
```

Raspberry Pi 2 - 1GB memory - 4 core CPU 900MHz - Blockchain on SanDisk Ultra Android microSDXC 128GB up to 80 MB/Sec Class 10

All other RPC calls through bitcoin-cli are answered promptly and correctly.
See also issue on jlopp/statoshi https://github.com/jlopp/statoshi/issues/19#issuecomment-171350739

{
    int nCheckLevel = GetArg("-checklevel", DEFAULT_CHECKLEVEL);
    int nCheckDepth = GetArg("-checkblocks", DEFAULT_CHECKBLOCKS);
    if (fHelp || params.size() > 2)
        throw runtime_error(
            "verifychain ( checklevel numblocks )\n"
            "\nVerifies blockchain database.\n"
            "\nArguments:\n"
            "1. checklevel   (numeric, optional, 0-4, default=" + strprintf("%d", nCheckLevel) + ") How thorough the block verification is.\n"
            "2. numblocks    (numeric, optional, default=" + strprintf("%d", nCheckDepth) + ", 0=all) The number of blocks to check.\n"
            "\nResult:\n"
            "true|false       (boolean) Verified or not\n"
            "\nExamples:\n"
            + HelpExampleCli("verifychain", "")
            + HelpExampleRpc("verifychain", "")
        );
    LOCK(cs_main);
    if (params.size() > 0)
        nCheckLevel = params[0].get_int();
    if (params.size() > 1)
        nCheckDepth = params[1].get_int();
    return CVerifyDB().VerifyDB(Params(), pcoinsTip, nCheckLevel, nCheckDepth);
}
static UniValue SoftForkMajorityDesc(int version, CBlockIndex* pindex, const Consensus::Params& consensusParams)