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

{
    UniValue result(UniValue::VOBJ);
    result.push_back(Pair("hash", blockindex->GetBlockHash().GetHex()));
    int confirmations = -1;
    
    if (chainActive.Contains(blockindex))
        confirmations = chainActive.Height() - blockindex->nHeight + 1;
    result.push_back(Pair("confirmations", confirmations));
    result.push_back(Pair("height", blockindex->nHeight));
    result.push_back(Pair("version", blockindex->nVersion));
    result.push_back(Pair("versionHex", strprintf("%08x", blockindex->nVersion)));
    result.push_back(Pair("merkleroot", blockindex->hashMerkleRoot.GetHex()));
    result.push_back(Pair("time", (int64_t)blockindex->nTime));
    result.push_back(Pair("mediantime", (int64_t)blockindex->GetMedianTimePast()));
    result.push_back(Pair("nonce", (uint64_t)blockindex->nNonce));
    result.push_back(Pair("bits", strprintf("%08x", blockindex->nBits)));
    result.push_back(Pair("difficulty", GetDifficulty(blockindex)));
    result.push_back(Pair("chainwork", blockindex->nChainWork.GetHex()));
    if (blockindex->pprev)
        result.push_back(Pair("previousblockhash", blockindex->pprev->GetBlockHash().GetHex()));
    CBlockIndex *pnext = chainActive.Next(blockindex);
    if (pnext)
        result.push_back(Pair("nextblockhash", pnext->GetBlockHash().GetHex()));
    return result;
}
UniValue blockToJSON(const CBlock& block, const CBlockIndex* blockindex, bool txDetails = false)